Heat Treatment - Crystal Weaving Foundation

Thanks, Larrin.

Here is a downloadable pdf - http://www.msm.cam.ac.uk/phase-trans/2003/strength.Young.MST.1994.pdf

Exciting to account for lbainite could play a conjunctive role in interrupt mart transformation mechanism. If merely interrupted then continue the same path, quenched blade at room and after cryo then room temperature should be at peak/max rc like all conventional ht would. Where cwf ht peak rc is after 275F soaked and brought back down to room temperature. Any insight or wag (your is more credible than mine) on cryo + 275F steps?

Larrin said:
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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There is spatial issue (mart takes more space than aust), otherwise we wouldn't have to deal with RA, right? Plus, aust to mart phase change is exothermic, so that extra heat/energy goes somewhere.
Larrin said:
Martensite is a diffusionless transformation; the laths grow nearly instantaneously.
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Larrin, at this point, if you were to speculate on his results (and not assumed as a fluke) using his HT protocol, terminology aside;
A: How would you describe the process differently?
B: What would you expect to occur within the alloy(s) giving as example, using Luongs stated temps and times?
C: Could you offer an opinion on why these knives show the toughness they do? If it is assumed that stated, or shown in video, the toughness is not a result of tempering or treatment outside his state protocol.
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What I am trying to reconcile here is that Luong may not have the technical aspects down, but if following the steps leads to a repeated result though the terminology differs, the result doesn't change.
A rose by any other name, and all that...

I can't follow directly what is going on, since this out of my league. But, if this were all to be viewed as sheer logged data via observed and hand written logs offered to the general public, and You were to make a knife using this and saw it for yourself, how would You describe the actions taking place if the results were comparable?
 
Larrin seems to be suggesting that bluncut's protocol may create an intermixing of bainite and austenite (the latter transforming to martensite) and this increases the durability (toughness) of the steel without impacting strength/hardness. This latter point, according to the cited publication from 1994, remains plausible up to 0.25 Vf bainite - the bainite acts as a tough binder and concentrates more carbon into the (eventual) martensite thereby compensating (or potentially overcompensating) for any potential loss of strength.

From wikipedia page:

607px-CCT_curve_steel.svg.png


Luong's steps abridged:

shallow hardening - fast cool to avoid Pearlite Nose, then begin step1...
...
s1: quench obj to 450-465F oil bath, slice around for 10 seconds, then stir around for 1 minutes...
...
Target for uniform 1F/minute drop in temperature...
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NJBillK said:
Larrin, at this point, if you were to speculate on his results (and not assumed as a fluke) using his HT protocol, terminology aside;
A: How would you describe the process differently?
B: What would you expect to occur within the alloy(s) giving as example, using Luongs stated temps and times?
C: Could you offer an opinion on why these knives show the toughness they do? If it is assumed that stated, or shown in video, the toughness is not a result of tempering or treatment outside his state protocol.
-----
What I am trying to reconcile here is that Luong may not have the technical aspects down, but if following the steps leads to a repeated result though the terminology differs, the result doesn't change.
A rose by any other name, and all that...

I can't follow directly what is going on, since this out of my league. But, if this were all to be viewed as sheer logged data via observed and hand written logs offered to the general public, and You were to make a knife using this and saw it for yourself, how would You describe the actions taking place if the results were comparable?
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A) It's a marquench where Luong is testing the effect of the cooling rate after the quench.
B) In a marquench you primarily get martensite formation but also tempering, some bainite formation, and austenite stabilization can also occur depending on alloy content. The extent of tempering obviously increases with slower cooling rates. We would expect very little bainite in tool steels and martensitic stainless steels but perhaps a significant amount in a steel like W2.
C) I can't speculate on how much toughness is being achieved relative to other heat treatments.
 
Uh-oh, not gonna be able to tell martensite from bainite via ESBD: http://www.ebsd-image.org/documentation/reference/qualitymetrics.html

The analysis of the microstructure of commercial steels is a common application for EBSD. Although diffraction patterns of ferrite grains (body centered cubic crystal structure) can easily be differentiated from retained austenite grains (face centered cubic), EBSD is incapable of separating martensite or bainite regions from the ferrite grains. Martensite or bainite are obtained by rapid cooling from the austenite phase leaving the carbon atoms (soluble in the austenite phase) trapped inside a body centered cubic crystal structure. This result is the formation of a metastable body centered tetragonal structure. The c/a ratio of the tetragonal lattice is very close to unity [3] and is therefore very close to a cubic lattice. This slight variation of the c/a ratio is undetectable in normal EBSD operating conditions. The crystal structure of martensite, bainite and ferrite are indistinguishable from one another.

However, the dislocation density of bainite or martensite is higher than that of ferrite. [4] The higher dislocation density deteriorates the quality of the diffraction pattern due to the higher lattice distortion. On average, diffraction patterns of ferrite therefore have a higher quality than those of bainite and martensite. This principle was verified via nano and microhardness measurements by Wu et al. [5]. The separation of bainite from martensite is more complex since the difference in their dislocation densities is smaller. Ryde concludes that the discrimination between these two phases could only be performed by “analyzing the directions of the carbide precipitates with a high resolution microscope”. [3]
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Good assessment with a+b, cwf ht w2 should be loaded with bainite, right? implied hrc should for sure less than 63rc, right? However my results W2 are normally 67+rc, which seem to contradicted this assessment. Any insights on 'why'?

What's your take on cryo & 275F steps for W2?

Larrin said:
A) It's a marquench where Luong is testing the effect of the cooling rate after the quench.
B) In a marquench you primarily get martensite formation but also tempering, some bainite formation, and austenite stabilization can also occur depending on alloy content. The extent of tempering obviously increases with slower cooling rates. We would expect very little bainite in tool steels and martensitic stainless steels but perhaps a significant amount in a steel like W2.
C) I can't speculate on how much toughness is being achieved relative to other heat treatments.
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Thanks Chiral but cwf ht cooling isn't the 'slow cool' curve. cwf ht step1 is to go below Ms(Martensite Start Line) and then 1F/minute cooling until near room temperature (3-4hrs or so).
chiral.grolim said:
Larrin seems to be suggesting that bluncut's protocol may create an intermixing of bainite and austenite (the latter transforming to martensite) and this increases the durability (toughness) of the steel without impacting strength/hardness. This latter point, according to the cited publication from 1994, remains plausible up to 0.25 Vf bainite - the bainite acts as a tough binder and concentrates more carbon into the (eventual) martensite thereby compensating (or potentially overcompensating) for any potential loss of strength.

From wikipedia page:

607px-CCT_curve_steel.svg.png


Luong's steps abridged:
Click to expand...
 
IMO - for edge tools require high keenness (less than 200nm apex radius), lower bainite is an undesirable attribute because ferritic presents and possibly cementites as well (although cementite might be super fine).

There is no such conventional 65rc 3v with duplex (large bainite% & martensite) microstructure. Duplex microstructure blades usually with hardness less than 60rc. Early on with my tinkering, I sure produced a few of them.
 
According to Prof Bhadeshia - BSED/ESBD (should) takes weeks to read by metallurgists and grad students. It took me more than a month (with helped from a metallurgist) to read some of my BSED images of BCMW samples.

The more complex microstructure, the longer it takes to decipher BSED, TEM, AFM images. Sometime can't even extrapolate 3d topological in 2D presentation.

Bainitic reacts (transform) poorly(for intended application) to welding. LOL - I followed & studies Prof Bhadeshia's bainitic stuff for 3+yrs now, so hopefully I know a bit or 2 about bainite. Earlier post - I did mentioned weldability of CWF ht. OK, maybe I was dreaming :D
 
Technical covers a few fields in context of this thread...

Here is a mathematical graph model for simple graphene - https://johncarlosbaez.wordpress.com/2016/08/06/topological-crystals-part-3/

My COG (combinatorial opt graph) model is for much more complex (more variables + spatial), except I mapped to COG so I can freely perform simulation in my head :) Are there technical questions - I need to think (or hand-waving) about?

Are there physics or chemistry aspects I goofed?

On metallurgy front - 1) I probably used some terms incorrectly 2) it would be great if we discuss at high technical level, only go lower when it's obvious that something over my head.
 
from your protocol, it looks like you quench down to just above the Ms, then cool 1F/minute. If Ms is ~400F, it'll take an hour to get to it.

How do you monitor/control the rate? Thermometer and lifting/closing the lid of the bath?
 
Chiral, excellent catch :thumbup:

If there only aust matrix (without embeded free carbon, alloys, etc), phase change to mart begin (not counting straddler few mart) around 480-500F. Above that temp main phase be bainite. Remember phase change is based on probability rather than 100% deterministic (recall the linked above about driving force, except apply to non-mart phases change as well).

Noted: above, I mentioned cooling as slow as 0.06F/minute for 3V & 52100 and didn't make a diff vs 1F/minute cooling, so lbainite sure didn't take over as conventional ht chart says it should. Sorry to [ip wall] here.

When ramp oil temp up, I use an analog thermometer. When cooling I either poke a hole through foil or use digital thermometer with long wire. Early on, I did open and close lid but learned better. Once, certain configuration meet 1F/minute cooling, I don't bother to check temp any more - just an alarm when to do next step.

chiral.grolim said:
from your protocol, it looks like you quench down to just above the Ms, then cool 1F/minute. If Ms is ~400F, it'll take an hour to get to it.

How do you monitor/control the rate? Thermometer and lifting/closing the lid of the bath?
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Thing came up with open-ended return date(s). So in the next few hrs, if you have questions for me, ask.
 
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bluntcut said:
Can anyone out there using conventional ht to produce 69rc for cpm-m4 & 10v? If no, why not. It doesn't matter if this sample decay in 1 second after hrc test. Follow up assertion usually - does 69rc m4 useful at all? It doesn't matter because you wouldn't know due to lacked of knowledge & experience.
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Just because they haven't doesn't mean they can't. There are other issues to contend with, like people that cut cars apart or break up concrete driveways with their knives. Yes, things like that are not knife uses, but when you offer a 100% guaranty you tend to make things a little tougher. For example, Busse Ht'd one original SHBM to 65 Rc. So this is a carbon steel with 0.5 to 0.6% carbon Ht'd to 65. And I am sure other makers have done this.

Playing with cooling rates is always a good idea and can net good results. This is nothing new, and there is a reason why there are makers out there doing 80 hour Ht's. Most of that time is in the transition between stages and soak time at certain points. I like what you are doing, it is fun to see the progression but this is by no means revolutionary.

However, what might be new and revolutionary is if you can do this to already Ht'd knives without affecting their HT. Not sure who would want to risk a proper Ht to find out though.
 
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bluntcut said:
There is spatial issue (mart takes more space than aust), otherwise we wouldn't have to deal with RA, right? Plus, aust to mart phase change is exothermic, so that extra heat/energy goes somewhere.
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A small part of RA may be the volume change and associated internal stresses, but the main reason for RA is the strengthening of the austenite by additional carbon and other alloying element. RA increases with carbon in solution at the austenizing temperature. This happens by increasing the overall carbon content of the steel in hypoeutectoid steels, or by dissolving too much carbide in hypereutectoid steels. The extra chromium and other elements in higher alloy steels further strengthens the austenite, making RA more of an issue in those alloys, even when carbon is not excessive.
 
bluntcut said:
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
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So by this I assume you are talking about the HCP iron? Based on the Wikipedia article, this would require internal compressive stress 3 to 10 times higher than most steels are capable of reaching without failure.
 
marcinek said:
Well, I happen to think if someone is claiming to make a "small contribution to science," then one needs to do a controlled experiment. If you change more than one variable in an experiment, like type of steel AND geometry, then what you have done is not a controlled experiment. It becomes subjective.

And there is nothing wrong with subjective results gained from experience, we give them all the time.

But they are just not science.
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Controlled and/or non-controlled experiments are both experiments of science. Having a controlled environment and factors do heighten the reality of the results you discover, but nevertheless, conducting an experiment in non-controlled situation, is still a test of science.


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