A1 tool steel heat treatment

B

Bono Kasapi

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Jul 4, 2017
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I was wondering how do I go about heat treating the A1 steel I came across this piece of A1 and made a knife out of it I'm not really familiar with air quenching I usually use steel that requires oil quenching and wanted to to know if I need to temper that knife in the owen or just air quench - thank you in advance
 
A1 tool steel? Never heard of it, doesn't seem to exist. How did you come to the conclusion that the steel is "A1"? A2 is a common air hardening steel, and O1 is a common oil hardening steel.
 
A2 is one of my favorite steels, along with D2 and 15n20. I had posted my A2 heat treat in another post so I thought I would post it here.

Oh ok.
I heat my oven to 1775° and hold that temp for at least a half hr to one hr to make sure the oven is all nice and even inside. I use 2 stainless pipes in my oven as blade holders and it also helps even out the temp as it's extra mass and the edge of the pip is close to the tip of the TC. Once the oven has soaked I put the blade into the oven between the pipes and close the door. I watch the temp on the controller and once it comes back up to 1775° I start the 45min timer. I find that if after you open and close the oven door if it takes a long long time for the temp to come back up then your oven was not soaked long enough. It should only take a min or so to come back up to temp. I quench between quench plate on my anvil using a quick clamp. I pull the blade out and it goes between the plates and I gently clamp down on it. This keeps everything straight unless it's AEB-L that stuff just seams to have a mind of its own. After its cold I remove the blade from the foil and go right into the cryo. Befor cryo it will RC test at around 62-63rc, this is not that accurate as I find that air hardening steels need time to reach there peak hardness. I leave the blade in cryo for 1hr, this is the amount of time it takes me to process another blade so once the next blade is done it goes in the cryo and the last one comes out. I have playied with cryo times to see what difference it makes and anything over 1hr does not seams to make a difference. I have soaked for 24hrs and it comes out the same hardness as 1hr blades. So take it out of the cryo and let them gently warm up to ambient room temp. I measure 66RC and like I said I had one come out at 67 after cryo. I then sort out where the bow is as even a straight blade will have a very slight bow. I then clamp them to a thick steel plate and put this in the preheat tempering oven.

remember not all heat treat ovens are the same, 1775° works great for me but your oven could be different then mine and be higher or lower actual temp then what mine is when it's set to 1775°.
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JT, I'm not sure that A-2 is really suitable for Cryo , that is the formation of eta carbides .Cryo is also typically a slow process , maybe 6 hours. When I was a kid we didn't have much in the way of carving tools but I was wishing for something that would go a bit longer between sharpening ! That was long before I was a metallurgist !
 
mete said:
JT, I'm not sure that A-2 is really suitable for Cryo , that is the formation of eta carbides .Cryo is also typically a slow process , maybe 6 hours. When I was a kid we didn't have much in the way of carving tools but I was wishing for something that would go a bit longer between sharpening ! That was long before I was a metallurgist !
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I know in the past the word on the street was cryo for D2 but not for A2. Nathan posted somthing a little while ago about somthing he came across regarding this. And my testing has seamed to fallow the numbers he posted.

"A2 does fine for edge stability (probably better than 3V), but consider your use of cryo and the effect that RA plays on edge stability. There is more RA than we used to believe.

I saw this the other day. From "Heat Treating, Including Steel Heat Treating in the New Millennium" (ASM Heat Treating Society) 2000.

A2 oil quenched from 1775°F had RA 16-18% (as quenched), 64-65HRC.
A single 400°F temper had no change on RA, but reduced hardness to ~60HRC.
A single 1000°F temper reduced RA to levels below X-Ray diffraction detection (<2%), lowering hardness to 56-57HRC.

A2 oil quenched from 1775°F
A -100°F cold treatment was applied to as-quenched sample, reducing A2 RA to 9% raising hardness to 65-66HRC.
A single 400°F temper drop RA in A2 to 4%, hardness 61-62HRC.

A2 oil quenched from 1775°F
immersed in LN for 3 hours, result was RA <2%, 66.5HRC

The problem with RA and possibly converted RA is weakness on a small scale and possibly reduced cohesion with surrounding matrix of converted structures. This is important for fine edge stability. This is low hanging fruit.

So, A2 does pretty well with edge stability, but not "out of the box", you have to process it for edge stability. Cryo is an important part of the equation, as is starting with quality A2. :thumbup:"
 
Ovens vary slightly, so this is the formula I personally use. Blades are ground basically to final dimension and finish, to the point all that is left is buffing. I use LS Starrett precision ground A2 if that makes any difference.
Blades are foil wrapped and placed in a cold kiln. I used to ramp the temperature slowly, but I switched to as fast as the evenheat will go a while back and couldn't tell any difference.
Start with a ramp to 1475 as a preheat, and hold it for a few minutes. Then ramp up to 1775 and when the alarm goes I'll let it sit for half an hour before starting to pull blades out. When the blades are pulled out I plate quench, and then let cool until room temperature.
I don't think I've ever had even the slightest warp with A2.
Temper depending on your desired hardness and your oven. I've noticed as much as a 50 degree difference between my evenheat and kitchen oven at the same setting. So start on the low end and work up until your desired hardness.
Whenever I use a new steel I'll usually make a few identical test blades with slightly different HT recipes and beat the crap out of them to see what holds up best, and what gives the balance of toughness and edge holding I look for.

A2 is very tough stuff and seems to work well with very thin blades. It's damn near impossible to make the edge chip with anything short of serious abuse.
In heavier blades it makes a very hard to beat chopper.

It's easily my favorite carbon steel, nice to work with, nice to HT, and very versatile. Everything in knifemaking is a trade-off, and A2 falls about where I personally like the tradeoffs to be.


I have ln2 for cryo, but personally don't use it for A2. I've tried it, but couldn't tell any difference in my testing. I can't see it hurting anything though, and your results may vary.
 
If your furnace goes to 1000C, you can heat treat yourself. If not, send it out. was used a lot at the office for fixtures, rails and guards. used more and more because it air quenches, don't need a quench tank.
 
Geoff Flato said:
Ovens vary slightly, so this is the formula I personally use. Blades are ground basically to final dimension and finish, to the point all that is left is buffing. I use LS Starrett precision ground A2 if that makes any difference.
Blades are foil wrapped and placed in a cold kiln. I used to ramp the temperature slowly, but I switched to as fast as the evenheat will go a while back and couldn't tell any difference.
Start with a ramp to 1475 as a preheat, and hold it for a few minutes. Then ramp up to 1775 and when the alarm goes I'll let it sit for half an hour before starting to pull blades out. When the blades are pulled out I plate quench, and then let cool until room temperature.
I don't think I've ever had even the slightest warp with A2.
Temper depending on your desired hardness and your oven. I've noticed as much as a 50 degree difference between my evenheat and kitchen oven at the same setting. So start on the low end and work up until your desired hardness.
Whenever I use a new steel I'll usually make a few identical test blades with slightly different HT recipes and beat the crap out of them to see what holds up best, and what gives the balance of toughness and edge holding I look for.

A2 is very tough stuff and seems to work well with very thin blades. It's damn near impossible to make the edge chip with anything short of serious abuse.
In heavier blades it makes a very hard to beat chopper.

It's easily my favorite carbon steel, nice to work with, nice to HT, and very versatile. Everything in knifemaking is a trade-off, and A2 falls about where I personally like the tradeoffs to be.


I have ln2 for cryo, but personally don't use it for A2. I've tried it, but couldn't tell any difference in my testing. I can't see it hurting anything though, and your results may vary.
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Have you ever checked the blades for hardness to see if you cryo has bumped up the numbers at all?
 
JTknives said:
Have you ever checked the blades for hardness to see if you cryo has bumped up the numbers at all?
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I haven't done a Rockwell test on that specific comparison. I have access to a Rockwell tester but it's enough of a pain to go use it that I do it infrequently. I do hardness tests when working up my formula for a new steel. I had already found what I liked for A2 before I set up with cryo so that test was a bit more subjective. Rope cutting, battoning through framing nails with a hammer, ect
Ultimately the Rockwell tests are more out of curiosity for me. I know how I want a blade to behave, and I'll work for that rather than a specific number. Personally I put more weight in real world performance, and I'll often carry a knife from a new steel for a couple months and use it daily before starting to offer it.
I use hardness tests more as a bit of bozo insurance to make sure I'm not leaving something on the table.
Next time I do some Rockwell testing though I'll make up some A2 samples to do a more scientific comparison.
I could end up being wrong on my more subjective test.
 
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I do. Apart from times and temperatures I treat it the same as I would 154cm or any other stainless. 309 foil wrap with a few square inches of paper in the envelope.

I will add that I saw you mention using a large pipe vise for plate quenching a while ago, and that was a brilliant idea.
I had a 6" ridgid pipe vise sitting around with no purpose. Now I use it constantly. Massively better than screwing around with clamps or sitting an anvil or bucket full of lead ingots on it
 
Yeah I wrap mine in foil to. I would wrap everything in foil if I could lol
 
JTknives said:
Yeah I wrap mine in foil to. I would wrap everything in foil if I could lol
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Main reason I don't really like working with oil hardening steels that much. Anti scaling compound, and cleaning off oil and various other residue before final grinding sucks.
I hate working with grimy parts so I always end up degreasing and wire wheeling oil quenched blades before going any further. The extra time and effort plus the unpleasantness factor makes the additional cost of A2 worth it for me. And that's not even considering performance at all.
 
I don't do much A2 anymore, but I always wrapped it. I have noticed that many posters giving HT advice on A2 and D2 never seem to mention wrapping it. Probably an omission of the obvious, but I wanted to check.

Geoff, that is the same vise I use. It works so simple it is nearly fool-proof. The two plates are about 3X3 to 4X4 cross section when stacked, so they sit right in the jaw teeth grooves. Only change I will do to mine when I eventually move it will be to permanently screw down the bottom plate.
 
Forgive the insanely newbie-ish question, but couldn't one wrap oil hardening steel for HT as well?
 
Getting the foil off and into the oil in time to harden it gets to be tricky, if not impossible.
 
I've done it for big (3"+ thickness) pieces in the past, but I wouldn't try it for something knife sized
 
Sorry if I wasn't clear, but I was thinking quench with the blade still wrapped.

By the responses I'm assuming the foil insulates enough to slow the quench below the needed speed?

What if wrapped and quenched in a faster quenchant (oil hardening in water, etc.)?
 
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