CPM 3V: High temper(1000°) vs low temper(400°) and sub zero quench

i have heard about some of the astounding things your 3v has done Jerry. and since i know that guys that have told me about it i have 0 reason to even doubt any of it.
all the 3v i have dont sept for 2 or 3 field knives that are over built from the get go have been neckers. as with you i see now and then a bit of edge flatting but not any chipping out even at 62rc the stuff is so tough that im swapping to PD1 to gain a bit more hardness and edge holding (im testing a 13 inch blade camp knife right now at 62rc )

chopps great and seems plenty tough so far again no edge chipping
 
I've never had any particular problem with corrosion with 3V, but I've seen it happen if the blade is not dried off when it's wet. I recommend a light oil to coat, then never think about it again. Stainless will rust, particularly if left in a wet sheath. The problem with 3V and rust is that if you do see a rust spot it will be sitting on top of a pit, not something you can just wipe off.

As for edge flattening, the only time I saw it was when one of my 3V swords went through a leg of beef, 9" of meat and 3" of bone. Small, about 5/32", flat spot where it first hit the bone, but no splintering on the outcut so it was still cutting. That is very hard bone. I am however certain the steel pipe chopper was flat on the edge by the time he stopped.
 
Try a test on a deer with your 3V sword .A deer leg bone is seven times harder than a cow ! LOL Blood is not good for steel as it promotes rusting.I clean the blade a best I can in the woods then place it in temporary cardboard so I don't contaminate my sheath.
 
Posts like that are why I don't much participate here. What does deer bone have to do with what I said? Ignoring that larger animals have bone more dense than smaller animals, the point was the condition under which I witnessed edge flattening. As for blood, never mentioned it. As for people tucking their knives in temporary sheaths while hunting, never met anyone who did that. Even so that had nothing to do with my comment on how 3V rusts. Amazing...

I quit. Have fun.
 
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...okay...

So a bit of random negativity there from a prominent maker directed toward one of the nicest fellows you'll ever meet (and a real actual metallurgist who is nice to have around here) ...but whatever...

Anywho...

I have not seen any modern analysis of the micro structures formed in 3V when following the manufacturer's suggested heat treat, but I have seen analysis of more common steels such as D2 and M2 which are not really that far removed and the most current metallurgical texts show considerably more stabilized retained austenite than was once believed to be present. And some of these texts have started to suggest techniques that some of us here adopted years ago that go contrary to the steel manufacture's recommendations. The manufacturer's core competency is making steel and not necessarily developing optimized heat treats to tweak particular properties for what is a very nitch application - edge stability.

Where most applications want dimensional stability, impact toughness in large sections and minimal risk in complex sections, our needs and aims are quite different. It should be no surprise when an optimal approach differs significantly from the manufacturer's suggestions. Just because something seems to work really well doesn't mean there isn't significant room for improvement.

Micro chipping and a tendency for edges to flatten out indicate a non-uniform micro structure that would not be a problem in a big stamping die or extruder screw but represents a significant deficiency in a knife edge. The fact is there are approaches to minimize this common deficiency in complex steels, and it deviates from industry norms. And precipitating a larger secondary carbide fraction and developing a carbon lean martensite is not the answer. So, to answer the question, yes, there are often very good reasons to avoid the secondary hardening hump.
 
Point of order Mr. Chairman, I mean Nathan. ;) Would it be a GOOD generalization to say the following. First, that higher corrosion resistance is a good thing. Second, that even in the case of a very tough steel like CPM 3V where you, as Mr Cashen might say, get what the chemistry will give you for the most part, would having fine, uniform microstructure, low levels of stabilized RA, say less than 5% and fewer large precipitated carbides leave you with a product that is optimally tough AND, if the steel is so inclined which I hear that 3v is, prone to better fine edge stability? I know it probably would;t be notable to the typical user or even to us, but when has that ever stopped us? ;)
 
Adding my 2 cents. A CPM steel like CPM154 is going to be tougher than the plain grade 154CM.Same recipe but different carbide size.
The matrix has to be strong to avoid having the edge roll over .The 'soak' is to dissolve as much carbon from the carbides during HT, making a stronger matrix.That will of course be different for different steels depending on carbide type.

BTW there are a series of lectures in metallurgyby H Bhadeshia, on youtube That may be helpfull in understanding various metallurgical concepts.
 
jdm61 said:
Point of order Mr. Chairman, I mean Nathan. ;) Would it be a GOOD generalization to say the following. First, that higher corrosion resistance is a good thing. Second, that even in the case of a very tough steel like CPM 3V where you, as Mr Cashen might say, get what the chemistry will give you for the most part, would having fine, uniform microstructure, low levels of stabilized RA, say less than 5% and fewer large precipitated carbides leave you with a product that is optimally tough AND, if the steel is so inclined which I hear that 3v is, prone to better fine edge stability? I know it probably would;t be notable to the typical user or even to us, but when has that ever stopped us? ;)
Click to expand...

Speaking in generalities, yes. There are of course exceptions. For example full cryo as a part of a rapid quench will certainly improve fine edge stability in any complex alloy with a tendency toward RA, but may not be appropriate in something like a sword where you have a thicker edge and want the ability to absorb impact. Also, in some applications a higher temper may improve edge retention in soft abrasive applications such as a cardboard slitter by precipitating additional secondary carbides. So I'm not saying that particular tweaks should be applied universally. I'm saying that the steel manufacturer and the industrial heat treat texts and heat treat shops have goals that differ from our goals and are not the end of the discussion.

When Keven talks about getting what the chemistry will give you, he's talking about being constrained by the chemistry of an alloy but leaving nothing on the table. Obviously this means avoiding pearlite and selecting the correct steel for an application, but also avoiding over stressing the matrix during martensite formation by techniques that induce autotempering for example. But that is in relatively simple steels. 3V isn't going to have a pearlite problem (unless you're doing something really weird with it) and the strain energy going into Mf is not going to be like a simple steel quenched in a fast oil etc.

Will the difference be noticeable to the typical user? Without a great deal of experience I don't think anyone can pick up a knife and use it and know whether or not it is performing to its best. I can't. In order for me to even somewhat objectively evaluate a steel and a heat treat I have to do comparative tests against "standards". So I have a set of standards, which are a set of knives of known qualities, that I send through a fixed set of specific cutting tests along side a test specimen that I want to evaluate. Only by comparing a knife to a set of known standards can I begin to honestly evaluate it. Simply cutting a bunch of rope and chopping on a antler doesn't really tell you the whole story unless you have fixed standards to compare against.

But to answer the question. Yes, a typical user can tell the difference if he has a standard to compare against. Will the typical user notice the difference in use? Probably not. Is there a difference? Certainly so. And even if most people don't notice it, some people will recognize it.
 
mete said:
A CPM steel like CPM154 is going to be tougher than the plain grade 154CM.Same recipe but different carbide size.
Click to expand...

To add to the discussion in what way I can, isn't this a bit misleading though in the way people typically conceive it? The actual carbides themselves aren't any smaller right? It's rather their aggregates that are? That is to say the CPM version won't have massive clumps of carbides bundled together.

If I have that right the above right, I'm pretty sure I read somewhere (maybe a Landes reference) that overall toughness isn't really improved very much (meaning we're not making 154CM as tough as 3V simply by going through the CPM process), but rather the average toughness is. To clarify that, if we're looking at toughness in terms of edge stability (lack of chipping, rolling, denting, etc) the CPM version will still do all those things, but the size of those deformities will simply be closer to the averaged size of the deformities (from small to large) seen in the non CPM version.

An analogy would of course be the same old concrete one which has large rocks in it. The CPM process doesn't change the rock size, but rather distributes them evenly so they don't clump together. So while the non CPM version may have an area very weak from a large clump of rocks, other parts, w/o the rock amount, will be more stable. Conversely, the CPM version will have a more uniform stability.

Anyway, not trying to stir any pots or anything, but just trying to add to the discussion. Looking forward to further posts
 
CPM both reduces carbide size and spreads them out more evenly. It's not perfect however. The smaller carbides can clump together, if given the opportunity. The amount of carbides will stay roughly the same. Of all the CPM pictures floating around, does anyone have any of 3V?
 
I think there's some misunderstanding there . When you look at CPM 154 vs 154CM , they both start with the same carbon content . The the two processes make either larger carbides like 154CM or smaller carbides like CPM 154, but the total carbide volume is the same. Look at the steel maker's websites including the similar European steels for photos of the microstrutures.
Some general comments about carbides. With large carbides fractures travel from carbide to carbide .With small carbides fractures tend to go at a random path.This will make the smaller carbide steel tougher.
Consider that we have two types of carbides in hypereutectoid steels. The carbides we start with , and carbides that are created during HT. When we bring the steel above critical temperature we dissolve some of the carbides [soak] .That carbon goes into the matrix . On further HT we form martensite . Then when we temper the martensite carbides are formed .
Now we find another interesting feature. Initially when the carbides are very small there is coherency between matrix and carbide .That provides significant strengthening !! We see this clearly in some of the complex steels where there is a hump when tempered at about 900 F.Here new , different carbides are formed.Higher tempering temperatures bring higher hardness but at one point hardness levels off the starts dropping.
What happened ? As the temps go up the carbides attract more carbon. As the carbides get larger the cohesion is lost because the lattice structure is no longer distorted and strengthening the matix.

. Landes points out that D2 carbides will, as the wear proceeds, break out and you end up with a saw tooth type edge. Smaller carbides wouldn't have the same effect.
Everything perfectly clear now ?
 
Mate - there is more. As you temper steel higher and higher, martensite looses carbon and its "deformation" and becomes softer and softer. With secondary hardness peak you got quite soft matrix and lots and lots of carbides.

It is great for industry tools, but is it really useful for hand held blades?
I do not think so.
BUT if we stick only to undissolved VC carbides from steel production, and epsilon carbines from low temp tempering...
do we really need highly alloyed steel? 3v is not high alloy, but many steels in industry is.

And about D2 - it is tougher after low (180-205°C) tempering. And why would I want to have serration of soft matrix, if I can get hard matrix and small carbides?
 
Yeah, I have a very rudimentary understanding as is, and whenever I try to play ball with my skillZ, it gets taken to the big boy courts, haha. Just enough to be dangerous or something like that.
 
The main reason I don't always take the manufacturers words as the "last word" is exactly like the instances in steels like D2..The industry standard heat treat is far less desirable for a knife than the heat treat many knife makers have adopted(in my humble opinion). The standard heat treat for d2 when used in a knife will often lead to a chippy blade or the old saying "takes a crappy edge and holds it forever"..When I tried the heat treat many knife makers have adopted with sub zero quench it was a marked improvement over the industry standard heat treat that was originally for dies. I did some blades in CPM d2 with the heat treat that Nathan uses and it was incredible..I loved it.
The point is I like trying different ways..I don't know if the 400° temper's are better, but I don't believe they are less from what Ive seen..I just think they may be easier for knifemakers to get right without fear of over shooting target temper temps and without having two kilns. So far Ive seen no brittleness issues at all with 400° tempers.
 
I hadn't mentioned eta carbides .They form on tempering after cryogenic quenching [ -300 F , liquid nitrogen ] .But they are very small and will have the cohesion that's so good.
 
There are far more YouTube lectures by H Bhadeshia than I thought .Go there and type in Bhadeshia for the list . Lots of graphs and photos which will be a help to learn metallurgy !!
 
Kentucky said:
The main reason I don't always take the manufacturers words as the "last word" is exactly like the instances in steels like D2..The industry standard heat treat is far less desirable for a knife than the heat treat many knife makers have adopted(in my humble opinion). The standard heat treat for d2 when used in a knife will often lead to a chippy blade or the old saying "takes a crappy edge and holds it forever"...
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Your thinking makes a lot of sense to me. Nathan has done a couple really interesting threads about D2 HT, and I suspect the same general idea is true for many steels. Like you guys are saying, most of the steels we use weren't designed with knives in mind, and neither was the standard HT.

Fascinating stuff, for certain.
 
i have been working with Carpanter steel and im hoping ot send the PD1 i have been playing with tested a bit more since im working with what woudl be a knife makers HT on a die steel
so far tho my testing has been at 2 quench temps cryo then a few temper temps (still looking for jsut right )
 
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