What about this heat treat for A2?

Kentucky

Kentucky

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Dec 13, 2008
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been doing carbon steels for a long time and now looking to delve into higher end steels..Been thinking a lot about A2..This is a heat treat that I have come across several times..What do you guys think? Any changes or opnions?
Foil wrap(is this nessasary?)
10 minute soak at *1475
Ramp up to *1750 soak for appx 45 minutes(3/16" thick)
Plate quench
Temper at *450 for RC60?
 
Double temper, possibly with cold/cryogenic. I prefer it harder, but the only one I've tried had edge issues (rolling, not chipping).
 
Yes, I feel that foil wrap (or scale protection) is necessary for any steel that you are going to soak at those temps for 45 minutes; it needs to be protected. SS foil works great with plate quenching steels.

For your reference, here's Crucible's data sheet for A2. Your plan looks to be in line with their recommendations except for they use 1775F and recommend 2 tempers of at least 1 hour each. As me2 pointed out, they also say that a freeze as a continuation of the first temper may help convert any retained austenite, and if so, you must follow with a second temper. It would probably work fine without the freeze as well.

A2

--nathan
 
I made a cutting competition knife from A2 in the past with excellant results and this is what I used:

10 minute soak @ 1200
ramp to 1400 & soak 10 minutes
ramp to 1800 & soak for 20 minutes
remove from foil pack & air quench (still air)
double 2 hour temper @ 500

Gary
 
I should have clarified but we always use two tempering cycles...
Now Cryo
I have read some use it, some dont and noone can relly say if it helps..Other than a article I read by lie nielsen that tests they did showed no difference in cryo treated A2 plane irons vs non-cryo treated plane irons..(Grew up in a woodowrking family)..Now i know that lie nielsen is a well respected tool maker..Though a plane iron and knife are slightly different animals.
 
On the freeze you are going to get into a flame war with it esp. on carbon tool steels.
If not cryo LN, do dry ice and alcohol 109-110 below. Bare minimum quench it between
frozen plates while still in the foil. I'm not going into it more on proof etc, lets just say I believe.
Ken.
 
Kentucky said:
I should have clarified but we always use two tempering cycles...
Now Cryo
I have read some use it, some dont and noone can relly say if it helps..Other than a article I read by lie nielsen that tests they did showed no difference in cryo treated A2 plane irons vs non-cryo treated plane irons..(Grew up in a woodowrking family)..Now i know that lie nielsen is a well respected tool maker..Though a plane iron and knife are slightly different animals.
Click to expand...

A cryo will help with the retained austenite on most alloyed tool steels. The more that the steel is alloyed then the more it seems to help. It doesn't do as much on your 10xx steels. Just remember to ALWAYS do another temper cycle afterwards.
A cryo is all time & temperature. (Dry ice will work just fine with a minimum of 4 hours.)

Gary
 
kc custom said:
On the freeze you are going to get into a flame war with it esp. on carbon tool steels.
If not cryo LN, do dry ice and alcohol 109-110 below. Bare minimum quench it between
frozen plates while still in the foil. I'm not going into it more on proof etc, lets just say I believe.
Ken.
Click to expand...

Thanks,Im glad to hear some advice on the sub zero quench..I have read a lot of conflicting thoeries and practices on it concerning A2..I dont have a problem setting up a dry ice/alcohol sub zero quench..
Oh and I dont do the internet argueing/ flame wars thing..My big full hillbilly beard proves Im older than 14 :D
 
Also what about a snap temp(*300 or so) after the plates but before the sub zero treatment?
 
I do D2, but the idea is the same. After plate quench, I make sure it is cool with a bucket of water then go right into a slurry of dry ice and kerosene. I am going to switch back to pure alcohol because the kerosene boils so bad when you add the dry ice. After about 1/2 hour soak in the dry ice I then go to the first temper, cool in water, then back in the dry ice for a second short soak, then second temper.

The dry ice slurry is about retained austenite. Complex steels have more trouble converting and will continue to convert as temps go down. I respectfully believe ( from reading metallurgist postings and my little experience of 100+ D2 blades) that a long soak in the slurry will not help. It will in liquid nitrogen, but that is more about carbide formation than retained austenite. I do the second short slurry soak because the first temper will start to convert a little more retained austenite and cooling it again will help the conversion. I only recently added the second slurry bath and it is hard to tell if it has helped much. But, I already have the dry ice slurry at that point and it certainly won't hurt anything. I am positive that the first slurry soak gets me some extra hardness. The length of the soak does not seem to add any hardness I have a small RC tester and test every blade. It maybe that the reason the tool maker saw no difference in performance is the retrained austenite helps maintain the edge in their use for some reason. When D2 is used for punch press dies and shear blade it is not super cooled and I believe the reason is the retained austenite helps maintain the dies under the extreme load pressures. It maybe that something like a chopper edge might benefit from a bit of retained aistensite as apposed to a thin slicer. Be interesting to make 2 choppers by each method and see. Just my 2 cents worth.

My full beard proves I hate shaving everyday. LOL
 
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Here is the HT recommended to me by Roman Landes for A-2.
Note where it says "Heat at a rate not exceeding 400 F per hour." To get maximum performance of A-2, I've found that directive to be a must.
For whatever it's worth, Joe Szilaski also advised me that all HT operations involving A-2 must be done with a slow ramp.
Thank you to Alpha Knife Supply for the link.

http://www.alphaknifesupply.com/Pictures/Info/Steel//A2-DS-Latrobe.pdf
 
There is a difference between 'sub-zero'[ -100 F] and 'cryo'[ -300 F] .While both reduce RA cryo also permits , on tempering, the formation of fine 'eta carbides' . Try it you might like it !
A2 is complex enough to benefit from cryo and should also be given two tempers . Always have a temper after cryo !
 
ib2v4u is correct in the fact that the martensitic finish point is reached in a dry ice slurry. The finish is done when the temperature is reached. No extra gain from extra time. It should stay in the slurry long enough for the blade to be completely cooled to the -100+/- temp of the slurry. 30 minutes is more than enough....... one/four/or eight hours will do no more hardening.

The most important part of the process is that the quench from austenite, and the dry ice finish be part of a continuous drop. You do the HT steps upward, then remove and plate/air quench, then cool to room temp ( just stick it in water after a minute in the plates), the put it in the dry ice slurry. Some folks do a snap temper at 300F for 30 minutes. With cryo, this is a safer method, but with dry ice most folks don't bother. The more the drop is smooth and continuous without delays from 1750/1800 to -100, the lower the RA and the better the martensite.

As said, cryo in LN is a different thing.
 
I know it sounds sort of snippy, but the answer is - " Do a quench and test the hardness". There are a lot of variables, and the exact result as quenched can vary 3-4 points. It could be anywhere from Rc 62 to Rc65. If all went well, Rc 64-65 is the target.
 
No, I understand..We dont have an easy way to do a hardness test..I planned on doing several samples and having them tested..i just wanted to know what I should be looking for..
 
That is a good idea. It will give you a baseline to work from in future HT. With a fair idea of how close to the book value your system does, you can plan the HT and temper pretty well without testing each one. Having a blade tested now and then is a good way to see if the results match the theory.
 
I was reading the fact sheet above and it meshes with one from crucible. It all talks about thicknesses of one inch or greater. With the typical thickness of a knife blade being less than a quarter of that, how does that change things?
 
Roman Landes also says that the reason salt works better is that you can soak it for less time. His premise is that the grain size of the matrix stays smaller and if you also manage to deal with the RA, that can only help when it comes to toughness and edge stability. So I would think that the trick would be to find the minimum soak time needed to get everything distributed all nice and such. That may be where the relatively narrow thickness of knives like objects comes into play. One thing that i do recall Roman saying about salt is that not only does it heat through more queickly and evenly, but it also stabilizes at the proper austenizing temperature more quickly than an atmospheric or vacuum furnace and that is important because soak doesn't start until you get stabilized. He also suggest that your first temper whihc comes after the cold treatment, should be done at a lower temp than the one that will get you your final tempered hardness and that you should do the water quench after the first temper like Jim suggested.

Edit. Roman also suggested a quench in properly heated oil (a medium speed one like Parks AAA or Tough Quench, not Parks #50, I would suspect because it does not need heating and is a pretty violent quenchant by oil standards.) even with the air quenching steels.
 
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