Testing W2 Hardness Quenched with Parks 50 and 9% Brine Solution.

samuraistuart said:
Jeff, like Me2 mentioned, normalizing technically is one cycle, not several. He is just trying to separate the correct terminology for future reference by others. Normalizing is done usually at least 100-150F above critical, one cycle, with an air cool. It is done to break up carbides that might have clumped together during previous forging/rolling, and to distribute them evenly. It is a one time deal. No need to "normalize" more than once, if it was done correctly.

Then we do "thermal cycles". This is really more about aus grain refinement than anything, putting more aus grain in a given area/volume, hence making them smaller. This is done usually around the critical temp, slightly above it, at it, and slightly below it. I suppose that ANY heat operation could "technically" be called a "thermal cycle", but for us knife makers, we understand that term to be limited to cycles at/around critical for aus grain refinement. After "thermal cycling" has been done, if no further machining needs to be done on the work piece, go straight to hardening. I asked Kevin what the best condition a steel could be in for hardening, he said either fine pearlite or upper bainite. Not a spheroidized structure, not a martensitic structure. That means that after the air cool is done on your final thermal cycle, you should have fine pearlite, one of the best matrices to harden from. I won't get into bainite, as that has a specific HT to develop.

Below "thermal cycle" temps is annealing temps ~1300s. For high carbon steels it is usually always best to spheroidize anneal if any further machining needs to be done. There will be no change over to austenite at these temps (below 1350f), so technically not much in the way of grain refinement here, mainly to soften things up. The mill that serves Aldo uses heavy spheroidizing on some of the steels, like 52100, and it is done at these temps for extended periods of time, hours upon hours from what I understand, with a very very slow drop in temp from sub critical on down to 900F or so. This causes large spheroidized carbides. Butter soft on tooling, but not so great to harden from.

Below annealing temps is stress relief temps ~1200s. Interestingly, if you take a martensitic blade (as quenched from critical) and "temper" at ~1200-1250F for a couple hours, you will fine spheroidize the steel for excellent machinability. This is also an excellent state to harden from, as it is extremely fine spheroidized, and does not need normalizing or extensive soak times to put the carbides back into solution.


Below ~1200s you get into the secondary hardening temps of tempering, post quench of course.

Your "assumption" that the subcritical temps you are using is what gets your W2 sample to harden properly is not correct at all. AAMOF, you do NOT need to do ANY subcritical temps to get a steel to harden after normalizing. Your test may seem to support your theory, but it is not correct by any means. Not meaning to hammer at you, just saying. Your 3rd sentence in the post above....again, no, subcritical cycling has nothing at all to do with normalizing. It is a completely separate operation for completely different purposes.
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Thank you very much for that very informative post Stuart because I couldn’t find anywhere on any posting what the difference between normalizing and thermal cycling was and I apologize if I have been using the words interchangeably because I thought they were referring to the same thing and now because of your very detailed explanation I know better.

Obviously you know much more than I and I appreciate you taking the time to explain to me this topic because I want to learn and make the best knife I can. And I do not dispute or challenge any of your information on this post and appreciate finally I understand exactly what the different temperatures and cycles do.

With that being said though it isn’t an assumption on my part that the addition of subcritical temps is what is getting my W-2 sample to harden properly it’s simply an observation. I am not disputing your information I am just saying my tests seem to show that I cannot harden W-2 unless I have subcritical temperature cycles and just normalizing alone won’t give me hardenable steel.

I have done two tests now without subcritical cycles and without them I cannot get my samples to harden properly. Honestly I don’t know how to reconcile the fact theory says that I do not need any subcritical temps to get a steel to harden when from several tests now it is evident that I do. Maybe this is just a very strange batch of W-2 but despite all the theory that is the reality.

I have done so many tests I even lose track of what I have done and have to refer to my notes to understand where I really am but in case it is confusing I do actually have two successful heat treats to give me consistently hard W-2 in the 66 to 67 range.

I can get in that range by either using 1650°F, 1350°F and 1250°F and not quenching or using 1650°F, 1550°F, 1450°F, 1350°F and 1250°F and quenching after every temperature. And I know that makes absolutely no sense but they are both systems that work consistently so I guess I can use this steel now. And I have been unable to get hard results without adding the sub-critical 1350F and 1250F cycles.

Basically I am just playing around now trying to see if I can get in the 68 ½ range which seems to be the maximum and also I am really curious about what makes this steel vary so much. So I appreciate your input because I understand much better what should happen but what is perplexing is that it doesn’t seem to be with this steel. But really thank you again for that post because it explained exactly what I have been looking for and been unable to find so I really appreciate the input.
 
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If you have a couple pieces to spare, you may try an 1800 to 1750 soak followed by air cooling to room temperature. One cycle, then quench from 1450 or so. That will ensure you have dissolved all the carbides that should be dissolved, and reformed evenly. That will also give you a larger grain size and increase the hardenability, perhaps allowing for full hardening with more consistency. This wouldn't be best for a blade, but let's get the hardening down first. 1 step at a time. Then again by time this is over you may have just tested up all your steel, so maybe don't do that.
 
me2 said:
If you have a couple pieces to spare, you may try an 1800 to 1750 soak followed by air cooling to room temperature. One cycle, then quench from 1450 or so. That will ensure you have dissolved all the carbides that should be dissolved, and reformed evenly. That will also give you a larger grain size and increase the hardenability, perhaps allowing for full hardening with more consistency. This wouldn't be best for a blade, but let's get the hardening down first. 1 step at a time. Then again by time this is over you may have just tested up all your steel, so maybe don't do that.
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Actually me2 I was considering just doing one normalizing temperature without any cycling and see what that did because so far I have always added other cycles to my normalizing. I want to do a couple other tests with the systems I have that seem to be working but eventually I may try that.
 
I just wanted to update my recommendations for how to heat treat W-2 from Aldo’s because after doing more tests I have slightly changed my process.

This steel needs to be normalized and also needs thermal cycling. The normalizing temperature I use is 1650°F. For thermal cycling despite conventional wisdom I find doing above critical temps do not aid in hardening but also do not hinder and also contrary to conventional wisdom and theory what is vitally necessary are sub-critical cycles; I use 1350°F and 1250°F.

And the change I have made is that I do quench after every temperature for both normalizing and thermal cycling. I was having good results not quenching at all and then suddenly I wasn’t getting full hardening without quenching. I did several tests with quenching and not and I always get full hardening if I quench after every temperature cycle. This steel is incredibly temperamental and I could get away without quenching but then for some strange reason I couldn’t so I do recommend quenching now.

So to recap this is my normalizing and heat cycling. I either do 1650°F, 1550°F, 1450°F, 1350°F, 1250°F quenching after each heat cycle after turning to black or I just do 1650°F, 1350°F, 1250°F and quenching after each temperature. I have found it is very important to include both the two lower sub-critical heat cycle temperatures and to quench after each temperature to ensure maximum hardness. I have been getting consistently between 66 and 68 on the Rockwell scale using these two methods.

I don’t really know at this point whether the addition of 1550°F and 1450°F improves grain refinement but they don’t seem to increase hardness. I find any deviation from this system resulted in terrible hardness usually below 50. I understand W-2 varies greatly so this system works with the W-2 Aldo currently supplies as I received this about two months ago. Good luck everybody and I believe this is the end of my posting W-2 heat treating tests because I really don’t think there is much more to gain hardness wise.

Now that I have my heat treat figured out I am actually going to make a knife! My first hidden tang Bowie!
 
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Hey Jeff,

Any updates on your W2 experiments? Did you make the Bowie? How did the blade test?

I am currently experiencing the same problems you had with poor HRC numbers for my W2 coupons.
 
Marc I was anxious to see the results of your test coupons :)
I keep thinking to myself -where is the point of diminishing returns for these steels....
anyway, I got a real Hardness Tester now if you need another check.
 
I'll take a picture of my results.

Edit:
Here you go Harbeer.
 
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I guess the question that comes to my mind is, did you get an as quenched reading? before tempering
 
"I guess the question that comes to my mind is, did you get an as quenched reading? before tempering"


Yes, the two samples at the bottom with a slash through the tempering info.
 
Yep, Parks 50 at 57˚. It was chilly in the shop. I guess I should have heated the oil to at least 70˚.

Thanks. You're right Warren. I thought about that after the fact. I'll try 1/8" thick coupons next. Also, I thought I had to grind off a bit of the surface because of decarb. But with W2 being a shallow hardening steel (and probably getting shallower with each heat cycle) I likely ground through what hardened steel there was to begin with.

Sorry Jeff, I didn't want to hijack your thread.

But since we are here, another question I have is: What is the best procedure to use when processing samples of shallow hardening steels for hardness testing? You have to remove decarb, but how much surface removal will take care of decarb without going through hardened steel?
 
70° is the minimum recommended temperature, as per the specs. I use it at 90°-100°F. W2 is extremely shallow hardening, much more so than even 1095 (.2% vs .4%), and Warren may be right about 1/4" coupons being a bit thick even for P50. It may thru harden them, if warmed up. I'm not sure about your last question. A coupon even 1/16" thick is going to have LOTS of hardened steel underneath a decarb layer. Decarb layer usually maybe 0.010" thick.

Also with coupons, make sure they are long enough so when you grab them with tongs, then heat doesn't sink out. Make them like bars, grab one end with your tongs, quench the other end and read that end. If you make them little squares...I would be worried about heat sink from tongs/vice grips/etc.
 
Sorry I haven’t done any postings lately but I have been doing a lot of millwrighting which is my regular job and haven’t had time for knife making or testing. So sorry i4Marc I haven’t gotten around to making that Bowie yet but I will eventually but maybe not until I retire in November. With the economy picking up I just don’t have time to devote to much of anything other than work which is good in a way but I do miss making knives and will definitely return to it again in the future more seriously after I retire.


I see others are having the same difficulty as me with W2; it is awfully persnickety but if you check my last posting that is the method I got consistent results with so if anybody’s having trouble I would give that method a shot. Anyway good luck everybody and hopefully I’ll be back at knife making after November. Or maybe I’ll get that Bowie made in the summer and if I do I’ll post pictures of the process.
 
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