Heat Treatment - Crystal Weaving Foundation

Luong, I applaud your innovation and testing. We need a lot more of this among knife makers. We do need to be cautious until more testing is done though.

The areas that I am currently working on are forging at controlled temperatures and properly conditioning steel structures in preparation for austenitization.

Hoss
 
Natlek said:
I'm almost completely sure that this topic is open specially for bluntcut . . . http://www.bladeforums.com/forums/showthread.php/1411476-Search-for-the-Magic-Heat-Treatment I apologize if I'm wrong .But what about the tests, what about the results that have been achieved ?? So , what members with metallurgy back grounds have to say about that ? What about Rockwell hardness bluntcut achieved in many steel ?
Can you DevinT achieve these numbers with regular HT ?

1084 HT that gets Rc68, AEBL blades at Rc65
Click to expand...

Just a quick note, those hardness values are right in line with achievable hardness for both those steels. The may not be common, but knife makers do some odd things.

I feel certain you are seeing the linked thread through only the prism of this thread. The types of things Larrin discusses have been going on for as long as you want to look back. There are quite a few makers that do/did things the way they do them, with many steps, and they don't see if some of the steps are really doing what they think. Some get good results, some get good results as long as they report the testing.

As for this topic, there has always been what I believed to be a language barrier issue with BCMW's knives (Bluntcut Metal Works). I have talked with him about it for a while on different topics and I've never been able to quite make out everything he's been saying, and have thus been reluctant to discuss it as much as I'd have liked. Many of the terms he uses have specific definitions, but the way he uses them makes it nearly impossible to keep up with what he's saying when he is trying to explain the principles and mechanisms he believes are at work in his results.

His results are what they are, and appear to be very good. I'm forming a plan to try to replicate them with an old blade I have here. However, until we can see some comparisons, I cannot say they are better than could be achieved with normal HT procedures.
 
Lost a bunch of my post. BCMW has made some very specific claims in terms of his heat treatment, and the burden of proof lies with the maker of the claims. Now, someone else may actually do the work and that's fine. However, he makes some very specific claims, like HCP precipitation following cryogenic treatment. The follow up link, from another member, references HCP iron that takes nearly 2,000,000 psi to form. I'm not sure if that is what BCMW is talking about, but if so, that is a specific and tremendous claim and requires proportional proof and repeatability. On the other hand, the known eta carbide precipitation following cryogenic treatment (actual liquid nitrogen temperatures, not just below zero or dry ice) could have a HCP structure. I find it difficult to keep up with what he is talking about, as I mentioned above.

Had he come on here and said "this is my procedure, and I get better knives from it. Anyone that wants can try it and let me know if it's repeatable. I don't know what's causing it, but I think I'm on to something," no one would have batted an eye.

Now, the expected microstructure is a mix of very fine lower bainite, and slightly tempered martensite, with eta carbides, and perhaps a bit of retained austenite. The 1 hour hold at ~450 deg. F. will form some bainite in some of the steels he uses. The slow cool to room temperature is a marquench, and produces slightly tempered martensite. Low temperature and short time tempering of quenched steels produces changes in the structure that don't typically show as a loss of hardness, but do show an increase in toughness. As an example, L6 tool steel has a peak in torsional toughness at 275 deg. F. It then drops off and recovers, but at considerably higher tempering temperatures. The cryogenic treatment conditions the martensite and permits the precipitation of extremely fine eta carbides upon reheating to 275 deg. F. Typical tempering temperatures are higher, but I think this will allow the precipitation of some of these carbides.

It's also worth noting that two steel specimens can have hardness readings of 66 and 68 and actually be the same hardness. The precision of many hardness testers is + or - one point, and these 2 would both be 67 +/- 1. There is a lot more variation in data than most people know.

I have used some of BCMW's knives and, however he gets there, he makes a fine knife. The only thing I can say negative is they took longer to rebevel than I'd hoped. They held an edge better than my comparison knife, though I'm convinced this was a sharpening issue, ie BCMW's knives took a better and more burr free edge from the same sharpening procedure, allowing his knives to out cut the comparison blade. He also makes an excellent handle.
 
me2 - just want a minor correction about cwf ht and done with this back/forth + BCMW pass-around knives didn't have cwf ht.

Perhaps, I need to be clearer and in bold

CWF HT STEP: quench blade to 450F oil and then cooling 1F/minute by put a lid on hot oil bath. NOT HOLD AT 450F for 1 hr.
 
Hi Bluntcut,

I am intrigued by your process, and am considering trialling it this weekend. I have some of Achim Wirtz's 125SC steel (a super clean German steel similar to White #1 / #2) that I would like to experiment with.

What exact process would you recommend for this steel in the simplest English so that we can get some more data points on this process.
 
Ah thanks for the correction. An hour long cool through that range can still make lower bainite in some of the steels used. The general trend holds but the exact amountsamounts will be different.
 
It would also be good if you could outline the pros/cons of this technique versus multiple quenching/superquenching for ultra fine grain refinement?

E.g. are there scenarios in which you would choose SQ over CWM or vice versa?
 
Simplified CWF HT template for shallow hardening (low Cr) steels (W1-2, 10xx, 52100, white#1-5, blue#1-3, etc...)

Pre-ht blade edge should be ~0.04" thick. Grind thinner after attained some experiences.

Aust & soak: at whatever temperature & time you are using now or use mfg suggested temp & time

s0: interrupt quench for 2 seconds in whatever quenchant you are using now or use mfg suggested quenchant
Goal is to cool the blade to below 1000F but avoid cool the edge below 500F, so you adjust time accordingly to achieve this goal.​

** quickly go to s1. Best if s0 quench tank sits next to s1 hot oil bath **

s1: quench blade to 450-465F oil bath, slice around for 10 seconds, then stir around for 20 seconds. Hang blade in oil bath and let it cools 1F/minute until oil bath cooled below 200F.

s2: Air cool the blade to 90F, take out & wash.

s3: Cryo for 4 minutes, take out & wash.

s4: Soak blade in 275F oil for 5 minutes, take out & wash.

Done.

joshiecole said:
Hi Bluntcut,

I am intrigued by your process, and am considering trialling it this weekend. I have some of Achim Wirtz's 125SC steel (a super clean German steel similar to White #1 / #2) that I would like to experiment with.

What exact process would you recommend for this steel in the simplest English so that we can get some more data points on this process.
Click to expand...
 
CWF HT covers Ms to Mf. So, Other pre-Ms processes are still applicable. Previous full quench is now interrupted quench <= that is the diff/change.

I would not use CWF HT: for steels with carbon < 0.4% and when seeking plate martensite and want high ra and brittleness and many other cases of which aren't really desirable for edge tools.

joshiecole said:
It would also be good if you could outline the pros/cons of this technique versus multiple quenching/superquenching for ultra fine grain refinement?

E.g. are there scenarios in which you would choose SQ over CWM or vice versa?
Click to expand...
 
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Thank you sir!

Is subzero likely to be satisfactory for a low alloy steel like this?



bluntcut said:
Simplified CWF HT template for shallow hardening (low Cr) steels (W1-2, 10xx, 52100, white#1-5, blue#1-3, etc...)

Pre-ht blade edge should be ~0.04" thick. Grind thinner after attained some experiences.

Aust & soak: at whatever temperature & time you are using now or use mfg suggested temp & time

s0: interrupt quench for 2 seconds in whatever quenchant you are using now or use mfg suggested quenchant
Goal is to cool the blade to below 1000F but avoid cool the edge below 500F, so you adjust time accordingly to achieve this goal.​

** quickly go to s1. Best if s0 quench tank sits next to s1 hot oil bath **

s1: quench blade to 450-465F oil bath, slice around for 10 seconds, then stir around for 20 seconds. Hang blade in oil bath and let it cools 1F/minute until oil bath cooled below 200F.

s2: Air cool the blade to 90F, take out & wash.

s3: Cryo for 4 minutes, take out & wash.

s4: Soak blade in 275F oil for 5 minutes, take out & wash.

Done.
Click to expand...
 
Subzero (~-100F range: mostly via dry-ice or compressed liquid co2) is probably sufficient.

Cryo is better because colder = higher structural compression(due to thermal contraction), which (hypothetically) sufficient to initiate/seed hcp formation process. Liquid hydrogen would be super cool :D

joshiecole said:
Thank you sir!

Is subzero likely to be satisfactory for a low alloy steel like this?
Click to expand...
 
Good piece of knowledge :thumbup: I agree - 450F to 390F temp range - bainite transformation might/maybe taken place for a small number of steels. 'might/maybe' because bainitic% if any, depends on skills of heat treater for these steels.

me2 said:
Ah thanks for the correction. An hour long cool through that range can still make lower bainite in some of the steels used. The general trend holds but the exact amountsamounts will be different.
Click to expand...
 
I chuckled to myself, this morning after a strong coffee, realized most readers probably missed a crucial exchanges between Larrin & I. This is the key point whether CWF applies to HT at all.

***
Larrin: Nonsense because 1. martensite conversion is mostly across boundary to boundary. 2. There is no driving force?
no scope head shot (gaming speak)​

Luong/I: conventional ht is not applied here
check your ping :p​
***

This is a visual view of Larrin's 1st reason.
https://www.youtube.com/watch?v=OQ5lVjYssko
If cwf ht matrix contained this type of transformation, he is right. Which mean, I got right result using wrong reasons. With 60nm-100nm resolution BSED & SEM should able to tell whether large % of this transformation present in matrix. If EM failed to discern, AFM is needed for sub 50nm resolution, which COULD mean cwf ht produced an unconventional microstructure.

CWF developed to avoid exactly that kind of transformation because of excess driving force for martensite conversion. This driving force - I didn't invented its metallurgical concept nor wording: http://www.msm.cam.ac.uk/phase-trans/2002/Driving.Force.MS.Metal.Science.1981.pdf
 
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I'm not sure how you'd avoid that transformation other than avoiding martensite entirely.
 
Cooling 1F/minute is cwf ht best shot to reduce driving force, PERHAPS interrupt the domino affect of mart conversion across the grain. IDK what ideal mart cell group length be. I envision interrupt this force by slowly allow aust change to mart, energy released as mart cells happened. In my mind, released energy focus at the front (lattice orientation) of the newly formed cells. More conjecture, aust cells in front received this energy + higher dislocation, so phase change to mart interrupted. Forward direction/orientation from newly formed mart cells has higher dislocation than orthogonal direction <= this is what I envisioned as 'weave', where spatial stretched interface along mart cells would PULL (start vs normally push by driving force) new mart phase change in orthorgonal or off-aligned direction. So round and round - hatch or spiral form an outter mart structure, while trapped pockets are RA.
me2 said:
I'm not sure how you'd avoid that transformation other than avoiding martensite entirely.
Click to expand...
 
Lowering the driving force for martensite transformation does not change how the transformation occurs. Once a martensite lath is triggered it grows (incredibly quickly) until it is stopped by something else, generally either a boundary or another lath. Slow cooling does not change the mechanism of that transformation. To change the mechanism of the transformation you would need a different phase, which at this temperature range would be bainite.
 
:thumbup:

If lbainite present (says 5+% range), wouldn't that lower macro indentation testing (hrc)? I usually aimed/got CWF HT w2 67+rc.

edit to add: I did tried cool from 450F down to 350F in 12hrs, 30hrs and 48hrs for 3v, aebl, w2, 52100. Same result hrc. I couldn't tell the different between super slow cooling vs 1F/minute cooling, that is why I advise 1F/minute cooling. From testing, 2+F/minute cooling showed higher brittleness.

In conjunction with 'different phase', can it be particles/carbides (high carbide particle count steels)? Can mart orientation drastically varying with this process or it is stuck with parent aust orientation?

edit2: going further (looking for limits), can free Cr/V/etc interrupt mart conv too? LOL - maybe going too far, into conjecture land.

Larrin said:
Lowering the driving force for martensite transformation does not change how the transformation occurs. Once a martensite lath is triggered it grows (incredibly quickly) until it is stopped by something else, generally either a boundary or another lath. Slow cooling does not change the mechanism of that transformation. To change the mechanism of the transformation you would need a different phase, which at this temperature range would be bainite.
Click to expand...
 
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Doesn't lower driving force equate to lower kinetic?
Larrin said:
Lowering the driving force for martensite transformation does not change how the transformation occurs. Once a martensite lath is triggered it grows (incredibly quickly) until it is stopped by something else, generally either a boundary or another lath. Slow cooling does not change the mechanism of that transformation. To change the mechanism of the transformation you would need a different phase, which at this temperature range would be bainite.
Click to expand...
 
bluntcut said:
:thumbup:

If lbainite present (says 5+% range), wouldn't that lower macro indentation testing (hrc)? I usually aimed/got CWF HT w2 67+rc.
Click to expand...
I don't think that a small percentage of bainite would affect the strength much, particularly as the bainite itself is rather high in strength. There is some evidence to show that some percentage of bainite can actually increase strength: http://www.tandfonline.com/doi/abs/10.1179/mst.1994.10.3.209
 
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