D2 TTT diagram & cryogenic treatment?

galadduin

galadduin

Joined
Dec 25, 2004
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As I have my new kiln, I did a full annealing to last knife lot (7 knives - 2 small edc, 1 paring, 1 folder, 1 dagger, 2 reed knives) all of them D2 to test this kiln. Tomorrow all the lot will be heat treated. As I dont have any dry ice or liquid nitro all I have a deepfreeze for now (I will get some equipment for this later).
I have a TTT diagram for D2 (found somewhere I dont remember) but not so acurate as far as I see. When I look to perlite nose I figure I have at least 1000 seconds - if not more... If this is the case air quench may not be forced or plate quench is not necessary. Just still air will be no problem to get them fully hardened - even I dont have to get them out of the SS folio... Am I right? Do anybody have a good TTT diagram for this steel. I always rushed to get them cooled to room temp, but rushing always generates disformations needed to be corrected during temper.

Also I know if I want them to perform best D2 must be sub-zero treated. I have 3 questions:

1: If not sub-zero treated, what percentage will be the retained austenite. What is the best austenisation temp to soak to minimize the retained austenite (I was soaking at 1050 C for 30 mins)?...
2: What will be the benefit to treat in deepfreeze? Will soaking at deepfreeze (-20 C) to a long time - i.e. 3 days - be beneficial?
3: Some articles say subzero directly after quench then temper, some say first temper then sub-zero. What is the correct procedure?

Thank you....
Emre ...
 
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Also I wish to clarify:
I would choose low or high temp tempers. For ex. 220 C temper will result somewhat same hardness as high temp at 530 C. But which do I have to choose - toughness & retained austenite-wise?
 
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As long as you harden from 1800-1875 F you will only have a small percentage of retained austenite. According to my book you have about 5 minutes to get below the pearlite nose.Plate quenching is very convenient and eliminates warping. After about 8 hours you won't get more benefit from cryo.I prefer the lower tempering temperature .Make sure you temper twice ! Deepfreeze will have a minor effect. Cryo can be done directly from quench thoug there is a small risk of cracking.
 
According to Verhoeven, the rate of quench effects corrosion resistance. I have tried to get a better understanding of the mechanism behind this. As best as I can figure, chromium carbides are forming on the way down, eating up free chromium. As I understand it, the faster you quench, the more carbon remains tied up in martensite and RA, ending up somewhere else after freeze and temper, but interacting less with the remaining chrome. That's my understanding of it...



While you might want to snap temper before cryo, if all you're using is deep freeze I'd go directly to the freezer to minimize retained austenite.

If you're not using cryo, you may want to stay away from the higher austenitizing temps to reduce retained austenite. A table I have seen shows something like 20% RA from 1850, which is enough to prevent a stamping die from changing dimensions much after HT (the reason the RA was originally desirable in D2), but prevents a D2 knife from holding a edge like it should


How'd I do mete?
 
In my book "Tool Steels" Roberts , a table of hardening temps vs retained austenite,they get only 7 % hardened from 1900 F.At 1950 it's up to 22 % .That's a big difference from your data !! That's a puzzle even if there is some difference in chemistry . With my data a double temper with cryo would reduce that to very acceptable amounts.. You won't remove all RA anyway ,and it adds some toughness.
As far as corrosion mechanism I would agree with Verheoven.
 
Thank you very much Mete & Nathan. This is very good info. I read and read the old posts and many other articles but I realised there is no consensus on most parts of HT process. The most clear and scientific explanations comes from Mr. Kevin, Mete and Nathan. The service of you three in this trade is priceless. Even then there is a little definitive procedure for us to follow.

It all comes down to what we expect from the knife. The "shop habits" plays a huge role also. This is the main obstacle on the path. I am trying to eleminate most of my bad habits mostly resulted from the crap articles (these were easy to understand, easy to folow). These "informative" texts were mentioning edge packing, magical quenchants, mystical HT techniques (without soaking the blade at aus. temps). As a novice you think you know enough to HT by reading these texts. At the end you actually make a knife which is your creation, cuts well looks well (fine perlite as Mr Kevin stated :) ). At this point you become ignorant as you define yourself as "Knife Maker".

I guess the main reason of this is lazyness (I've been there). From now on If I want to be a real KnifeMaker I will have to have a filter; catches the crap from the information and ignores it. Read more experiment more....

Thanks again...
Emre

PS. I'll try high temp temper for 3 and low temp temper for the rest of the knives. I'll test them and post the results...
 
Thanks Emre, but I shouldn't be listed with the other two. At least not on HT stuff. Kevin and mete are the real deal, and you're right, their service to this forum is very valuable.

Mete, the table I'm referring to was something I found on the internet and I don't recall who published it. I'm sure your data is more likely to be correct.
 
You should go as cold as you can as soon as you can from the quench to get the minimum retained austenite. -20F is better than 70F. 1850F will give high hardness and low retained austenite.
 
By the way all I use to do my cyro is a galvanized bucket that I have wrapped with fiberglass insulation with about enough acetone to cover the blades well., I then stick in about 4 lbs or 2 kilos of dry ice and cover with more insulation. Anywhere that does fiberglass work should have the acetone and many grocery stores have dry ice. I am sure it is around somewhere, even in Turkey. How much it helps I am not positive. It doesn't hurt. I love my D2 blades.
 
There are dry ice suppliers Istanbul, Izmir etc. But no supplier near my town. At least the transportation will take 5 hours to my shop, I'm backed off to buy for this reason. ib2v4u how much time I have to transport them and can I keep them in an Insulated container for later usage...
 
I'm not familiar with that type of graph.We don't even use the term lederburite any more ,in fact not for many years..... Note that they don't mention cryo .
 
Mete,

I wonder if you and I may have been looking at similar data and drawing different conclusions about retained austenite in D2 because we didn't discuss the tempering temperatures being used? I frequently make special purpose knives that lead me to use lower tempering temperatures where retained austenite does not decompose in tempering. I have no way of measuring retained austenite, but charts I have seen indicate that D2 austenitized at moderate temperatures can have upwards of 20% RA unless one resorts to using the higher tempers to decompose it (which has down sides if used in a knife). I would be interested in knowing what your charts show for D2 quenched from 1850 to room temperature (no cryo) and tempered to only 475?

This chart shows 18% from 1870 but doesn't state cooling rate:

d2ra.jpg


Here I'm going from information scoured from the internet, which is not always reliable...
 
Oh man, it is from uddeholm inc. data sheet. This graph must be reliable as a rock as this company is one of the steel giants of Europe. Means, with a proper HT, 1020C (1870F) aus soak temp, and 475 C (887F) tempering you will have 60 HRC and minimal retained austenite (about 10%). Mete is there a transformation right after 400C (752F) at tempering? Seems a great decline from that temp at temper happen for RA - probably decomposing as Nathan suggested...
http://www.bucorp.com/files/aisi_d2.pdf

Also according to graph, it would be interesting to see a 58 HRC almost 0 RA at 525 C (1022F) tempering..
 
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Let me try to clarify this. Look at both the 'Tempering Graph' and the 'Hardness as a function of austenitizing temperature'. The second one shows clearly that retained austenite is proportional to austenitizing temperature.That is basic for high alloy and high carbon steel [tool and stainless steels] .This is due to the greater amounts of alloying elements dissolved at the higher temperatures. The retained austenite vs tempering temperature shows that for D2 the RA you get from hardening is not reduced until you get to about 800 F !
You won't remove all the RA and it will give some added toughness. For knives ? I think I'd keep the hardening temperature 1825-1850 F and temper at 400-500F. This would minimize RA on hardening and you wouldn't have to worry about reducing it by tempering. Do some experiments.I wonder what secret recipe Dozier has developed ? I'd also like to know how different CPM D2 is ?
 
Thank you Mete, I'll experiment around these issues. How would you test a knife (without any microscopes or X-Rays) to see what is the effect the tempering temperatures and hardening temps. RA wise???
For example would any toughness (break angle) test or wear resistance test reveal any fact about retained austenite percentage. Would any brittleness mean the percentage is too high or lover wear resistance mean. I will test these as D2 is the most available steel I can find around, and I'm a bit serious to be a decent knifemaker. I have to get familiar with my favorite steel... Experimental wise, any suggestions are welcome...

Thanks again,
Emre
 
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