ATS-34 HT Sample

R

rlinger

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Mar 29, 2002
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An ATS-34 8 3/4 OAL hunter; tapered 5/32 thick w/15 thousandths edge

(special thanks to Kit Carson for rightly advising me to use lower end tempering ranges for martensitic stainless steels)

Notice the lower temper temperature from that of my previous ATS-34 HT's - and no lowering of RHc value. In fact it tests a little higher than I wanted which can be tweaked by adjusting the austenitizing temp.. Being a secondary hardening steel I would have thought my RHc would have been closer to 58 even with the deep cryo.
------------

Equalize: 1250 F. - 7 minutes

Austenitize: 1965 F. - 25 minutes

Rapid air quench (a small vertical wind tunnel) to handling temp.

Remove foil

Deep Cryo (without delay but after cooling to room temp.): 12 hours

Still air warm to room temp.

Temper (without delay): 600 F. - 2 hours 15 minutes

Still air cool to room temp.

Temper: 600 F. - 2 hours 15 minutes

Still air cool to room temp.

Rockwell test. Results: 60 RHc (three sample average taken just behind front bottom of bolster area)
----------------

RL
 
Thanks Roger!

You know there is one thing missing, I think,: The ramp rate from 1250 to 1965. I assume you don't use 2 ovens, so there must be some delay. How long does it take to get there? At a ramp rate of 700 degrees an hour, that would mean your steel is in there for an hour and 32 minutes.

Or do you remove the steel after the equalize while the oven gets up to temp?

Steve
 
I see where you are going I think Steve

it's been My experience that if I leave 154CM
(very close to ATS34 in heat treating)
in for more that 15 mins at 1950 it will end up harder (the longer
soak the harder the Rockwell)
therefore I'd have to raze the draw down temp to reach the pre determined Rockwell I was shooting for..
sound good??
nope,, not a good thing if left to long, it will open up grain
and makes for a not so good looking mirror polish
it will have little white spots all through it.:mad:
this is IMHO why your still at 60 r at 600 deg draw down.

the deep cryo I don't think will change your rockwell but it will
help in edge wear as if it is harder.
if I said that right to under stand it.:(
 
Steve, I really haven't timed the ramp duration from 1250 to 1965 F. on my Even Heat. Its not real long and I would guess about 15 to 20 minutes. I may be off 5 minutes or so. Maybe I'll fire her up and time it this evening.

So far I've had no problems acheiving a consistant mirror polish on the ATS-34 steels. In the beginning I was austenitizing it for as much as 40 minutes.

According to the Crucible tech sheet 154CM can become harder with deep cryo. Perhaps I should HT a couple test pieces together and test one cryo-ed and one without, just to see.

RL
 
Thanks,

Just to make sure I have it right:

You pop it in when the temp is 1250. Wait for 7 minutes. Then change the temp to 1965. AFTER it reaches 1265 you wait another 25 minutes.

So the total time in the oven is about 7 + ~20 + 25 = 52 minutes.

Steve
 
Its longer than that. I put the foil wraped blade in the oven, edge up, before starting the oven. It is in there when the oven is at room temp. If my ramp speed was real slow I wouldn't want to leave in at 1965 F. for 25 minutes because the steel (ATS-34) begins to austenitize at about 1850 F. or a little less.

Roger
 
Your soak time at 1965 sounds awful long to me. Haven't done any ats 34 for awhile but the sheet I have says 15 minutes for 3/16" steel and less for thinner. I used to run mine at 1900 and I'd get 58rc. The one time I ran at 1950 the foil welded to the blades, that was a real pisser....
 
I have been getting very good results as far as sharpenability and edge retension with the 25 minute soak time. I would not at all be opposed to trying it at a shorter soak time so as to learn more about it. No doubt I will as time goes by.

Crucible's data sheet for 154CM says this about hardening: "Austenitize: 1900 - 2000 F., hold time at temperature 30 - 60 minutes."

RL
 
You need to find out what size material there running for that length of time. If I remember my Paragon oven instructions gave me the recipe I felt more comfortable with. I had also got a speck sheet from Texas Knifemakers that called for the 1950 for 15 minutes for 3/16 material but it also said to step it down for thinner material. I had found out the longer I did the stock removal the more different recipes there were for the same steel. I never did the cyro except for a few times with actone and dry ice and would pick up a couple points more hardness afterwards. I guess it all depends on what you feel comfortable with and what works for you.....
 
Roger
Mine was a worst case,, I left it in 1950 for 2 hours

yours was in for longer then 15 min and you tempered at 600 deg
and still had 60 Rockwell right?

try it for 15 min (put in ) at full temp and then draw at 400 deg and see if you get the same Rockwell
if you do you'll see what's going on in a long soak time.
yes I will say deep cryo will help the rock some but I'm saying it's the soak time that makes more difference in the rockwell.

I can't explain in type what I mean to tell you about cryo and Rockwell. it's got to do with
easier sharpening at a lower Rockwell and keeping the same
edge holding ability as if it was harder :confused:
that make any cents.:confused: :)
 
Raymond, since they do not specify the hardening time as a per inch rate I presume they mean it as: after the steel obtains uniform temperature. They do not specify on the sheet I have.

Peter, thanks. You helped.

Dan, I will do as you suggest. I will post the results. Since the cryo takes so long I may have something by Monday. I will do identical samples of the same steel and size from the same bar stock. One deep cryo-ed. One without cryo. Both oven tempered the same - at your suggested 400 F.. 15 minute soak at 1965 F..

Yes, cryogenic tempering transforms retained austenite. That is what you ment by better edge holding.

Steve, I just timed some ramp rates. Here is what my Even Heat just did:
----------
Room temp to 1250 F. - 29 minutes

1250 to 1860 F. - 45 minutes

1860 to 1965 F. - 13 minutes

I put a couple small blocks of steel in the oven.
----------

RL
 
Okay, I have two sample pieces of ATS-34 from the same bar stock as the blade was made from. I have both samples, side by side, in the same foil packet and the packet is in the oven now. I will duplicate the recipie at the top of this thread with these exceptions: The austenitizing soak time will be 15 minutes, one test piece will be cryo-ed and the other not, the tempering temperature for both temper sessions will be 400 F.. To do it right, as I see it, I will need to temper one test piece tonight as the other is in cryo. Tomorrow I will temper both together and then the one in cryo by itself so that both will be double tempered. I believe this is essential since I do not want one setting at room temp. overnight without being first tempered. All tempers will be performed in the Even Heat and the steel will only be placed in the oven after the oven has had time to stabilize. Just the way I did it before.

I am going to go out on the limb and guess the Rc now. I guess the one in cryo will test 59 and the one without 58.

I love this stuff. Heart-Heart.

Roger
 
Okay, I have gotten the one without cryo double tempered and tested. The one that was deep cryo-d is in final temper right now and will be tested in a couple hours.

I have taken 8 Rockwell samples of the one not cryo-d. They are:

58.9
58.2
58.8
58.2
58.8
58.3
58.7
58.2

The average RHc for the one not deep cryo-d is 58.5

This is amazing in that the Crucible data sheet specifies that I should expect a RHc of 59 for that test piece if I had oil quenched it. I rapid air quenched it. So the process I used tracks the data sheet results.

Now, just as interesting, the data sheet is telling me to expect a RHc of 62 for the one cryo-d (if oil quenched). Lets see if that one tests 61 to 61.5

I'll post the results as I learn them.
 
Here are the test results of the sample test piece that was deep cryo-d:
------

62.2
62.2
62.1
62.2
62.5
62.4
62.0
62.2

For a 8 sample average of 62.2 RHc, just as the Crucible data sheet told me to expect if I had oil quenched. I rapid air quenched.
-------

Notice how much tighter the tests are than that of the one not cryogenically treated. The piece appears more uniform in hardness. That is pretty good 'at first glance' proof of retained austenite being transformed by cryogenic tempering. Amazing.

There is an approximate 3 1/2 point difference between identical test pieces heated treated identically except that one was not deep frozen.

Here is what was done:
-----
Equalize: 1250 F. - 7 minutes

Austenitize: 1965 F. - 15 minutes

Rapid air quench

Deep Cryo one piece - 12 hours. Temper at 400 F. the other piece for 2 hours 15 minutes

Temper both pieces - 400 F. for 2 hours 15 minutes

Temper the cryo-d piece - 400 F. for 2 hours 15 minutes
------

Both pieces came from the same ATS-34 stock and were cut equal in length and are 5/32 inch thick. Both were placed side by side in the same foil packet. The packet was air quenched in a manner as to provide equal air flow over both pieces at the same time. The only real difference is that one was deep cryogenically tempered and the other was not. Both pieces were Rockwell tested using the same tester.

RL
 
One very interesting piece of info, Roger, would be the as-quenched hardness. My guess is that the test pieces had low hardness (56-58 or so) out of quench, and the hardness came up dramatically with the cryo converting the retained austenite. I have seen this again and again with ATS34.

Actually, dry ice acetone will convert the austenite, but supposedly the change in carbides at ultralow temps confers additional benefits.

The questions then become: "Is it imperative to get maximum hardness at quench?" "Does retained austenite conversion via cryo post-quench impart the same characteristics?" and "Is absolute conversion to solid solution of all alloy elements the best for a knife blade, or is there a better 'mix' preferable versus 'conventional' HT 'wisdom'?"

The more I read the less I know. :D

One thing those of us most intruiged by the minutae of HT need to do is get some ceramics cones and make sure our furnaces are actually at the temps we are discussing. Thermocouple probes are only accurate to about +/- 3% at these temps; that's over a 100F range at 1900F. There are also significant deviations from the set point positionally within the furnace. The engineer at Paragon actually thought that if I was within 100F of the setpoint, that was just fine. I am going to get several temperature cones and set them in sets at different points within my furnaces to try and get a better idea of how accurate these things are. I'll report back, eventually.

Nice thread and nice work Roger. I don't think the austentitic stainless steels have been studied near enough in terms of knifemaking.
 
So it looks like if you raze the temper temp 100
(at 100 less than the first time) deg's and with the less time in the hardening temp (15 min.)
you'll end up with the same results as you had
with the longer time in 1965 with a higher draw temp..

I use 1950 with a strong 425 draw.
so my results will be a little different, about 58+ Rockwell.

good job Roger:)
 
Dan, I do know I don't want my hunting blades at 62 RHc. I think I should maybe try a 600 degree temper after cryo but drop the hardening soak down to 15 minutes, as suggested by you more experienced makers. I thinkst I might like that kind of cooking. I should still see 60 and if I want 58 - 59 I could drop down to maybe 1940 F.. - whatever -

Fitzo, actually the Crucible data sheet specifies 61 for as oil quenched from 1950 F.. 63 if cryo after oil quench. It should be important to remember that the data sheet I reference is for 154CM and the test pieces are of ATS-34.

The hugh difference (I did not expect it to be more than a point and a half) by deep cryo amazes me. Well over 3 points is dramatic and had I not done it myself and knew all other things were equal I would be skeptical.

RL
 
I am not surprised by the increased hardness with the cryo. I have seen it be as much much as 5-6 points when I had a crappy quench on blades I had a heckuva time getting out of the foil bag to quench, and thus too much time slow-cooling prior to quench. Hardnesses as low as 55 or so out of quench, increasing dramatically with cryo. I have gone to aluminum quench plates (6x12x3/4"), bag and all, with a compressor-air blast between the plates. I am very happy with them, getting essentially the same hardness as Crucible claims it should be, prior to cryo.

I guess my point is that, IMO, from the "text book" viewpoint, one needs to attain max hardness, ie, that "63" Crucible quotes, and then temper at the appropriate temp to get the final number desired. (BTW, the Paragon guy told me that at tempering temps, their furnaces may be as much as 100F different than what the meter says, so these temps are pretty much reproducible but specific to each furnace. They won't necessarily translate to another furnace.) That is why I always check as-quenched, and then post-cryo Rc before I ever temper a blade. Anything less than that 63 means that we haven't gotten complete austenization and martensite formation. Tempering temps well below Crucible's stated data means the max hardness is not being achieved prior to tempering.

Is that a bad thing? I honestly don't know, and I believe that's the $64,000 question in terms of stainless knife blades. The fact that there is a very non-homogeneous environment in edge-quenched low-alloy steels means there are characteristics that we don't fully understand when it comes to knife performance. It goes beyond just having a martensite edge and pearlite spine, especially in a alloy steel like 52100.

Dan's method sorta deviates from the published formulae (short soak times, putting the blade in at high temp for only 15 minutes total, then a lower tempering temp than one would expect,if I understood correctly what he was saying), and yet he is obviously getting good results or he wouldn't be doing it regularly. There is definitely more going on in terms of knife performance than "conventional HT wisdom" suggests. It is very interesting to try and integrate all of these differences in methodology to try and understand what is happening in the stainless steels.

Thanks, guys, I really enjoy these threads.
 
Great information Roger. No wonder I hear cryo is essential in ATS-34. At least it does make a big difference. I should say I can see why some makers feel this way.

BTW I'd like to add this to your recipe. Maybe it's me, but I think it's significant:

------
Equalize: 1250 F. - 7 minutes
Leave in oven 58 minutes while temp raises
Austenitize: 1965 F. - 15 minutes
Rapid air quench
Deep Cryo one piece - 12 hours. Temper at 400 F. the other piece for 2 hours 15 minutes
Temper both pieces - 400 F. for 2 hours 15 minutes
Temper the cryo-d piece - 400 F. for 2 hours 15 minutes
------

Steve
 
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