WTF! This isn't supposed to happen!

T

Travis Fry

Well-Known Member
I recently made a nice blade from some san mai I got from a very reputable source that will remain unnamed. It's wrought clad CruForgeV, and I soaked at 1525 for 10 min or so before quenching in an oil from Maxim that I don't remember the name of but which is roughly comparable to PArks 50. The results are below. FUnny thing is, the weld between the layers held. It was the core itself that failed and split, as you can see in the 3rd pic. Also of note, the pictures show the results as they occurred, without any assistance from me, AFTER the blade was already cool to the touch.

Anyone have any ideas?

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That's a beauty.
Just judging by what I think I see in the pics, it looks like the core was 2 pieces with a bad weld maybe ? Major delamination, although the steel looks awful smooth and clean in the last pic. I don't think the oil is the problem, Cru-v is pretty close to W-1, water quench tolerable (supposedly in larger cross sections). Looks like it needed MAJOR normalizing. Keep us posted if you solve it.

Rudy
 
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Looks like that was 4 layers, not 3. You'll have to take it up with your supplier as that's just my amateur take on what the photo shows. Perhaps a little cleanup on the spine (what's left of it) and an etch to show any layers where it's not split?
 
Thanks to Mike, I may have figured it out, though this is an off-the-charts extreme example. I'm going to talk to the san mai maker tomorrow, then will post an update with conclusions. I'd love to see some of the metallurgically gifted chime in to confirm or disconfirm my suspicions.
 
Travis, when you get to the bottom of it if it was your error feel free to take it in the chops and explain to us what happened ;) ...I really don't want to do that to a knife myself, I've bent, broke, and crispy-crittered a few but this is something new.
 
That thing obviously had a deep rooted desire to become a butterfly knife. Saw it, right off.
 
Lagrange said:
That thing obviously had a deep rooted desire to become a butterfly knife. Saw it, right off.
Click to expand...

I disagree. I think it's the Conjoined Clip Knife with his and her handles... ;) Sorry, couldn't resist. But it's the first time I've seen this in my limited amount of time as a maker and I think it is wild!
 
As someone who does a LOT of forge welding, I can tell you two things....

1. Never try to laminate two steels that have such wide expansion/contraction characteristics......they do not expand or contract at the same rates when heated and/or cooled.....and more times then not, something will "give".

2. Cruforge DOES NOT play well with others.....by that I mean that it is difficult (to put it mildly) to forge weld it cleanly not only to other steels....but especially to itself, which is what I see in the photos.

It certainly looks to me that there were two pieces used for the core. I could speculate on all kinds of things, but my instincts tell me that its more a "compatibility" issue, that wasn't taken into consideration when the billet was conceived.
 
Ive had that happen with L6 san mai..The exact same thing..The core steel itself split in two..Ive sued a lot of wrought and 1095/1084 with no problems..the only time I ran into problems was with a higher alloy steel..Ive done all kinds of file steel(1.28% carbon) wrought/mild steel san mai in the past with no problems what so ever..
 
I can testify that Cruforge dont play well with others. I have never tried to forge weld it to itself.

I have had some success laminating it with stainless cladding, as well as doing it with a high carbon damascus cladding. Yet in the same respect. Welding it is only half the battle. I am 1 for 3 heat treat said billets. I think I am narrowing it down and should now be able to heat treat it with a little more success then the first few tries.

Its wild stuff for sure!

My money is one a single piece core that simply tore itself apart after quench. As I said Cruforge is wild stuff. and does present unique challenges as a stand alone steel, let alone a Wrought cruforge sandwich.. :) On paper the stuff looks pretty simple and straight forward. But in real life its been a challenge for me.

That said. I hope you get everything worked out sooner then later and have better success on the next one!
 
CruForgeV is not all that close to W1 more like W2 if any of the tool steels. It also has some chromium and, as Ed pointed out, that can make it rather difficult to weld due to chromium oxides building up on the surface of the steel. I would bow to Ed on his estimation that there were two pieces of CruForgV partially welded together that sheared in the quenchant. I've also read where some knife makers experienced a layer in the san mai or damascus shearing through a layer of steel. I think that L6 was the culprit under discussion then.

Another thing to consider is that the oil might have been too fast. CruForgeV is not a shallow hardening steel and the wrought won't harden to any degree so something as fast as Parks #50 might have put too much stress on the blade. Just a thought.

Doug
 
As one of the great radio personalities of all time used to say, "Now it's time for the rest of the story... "

First of all, contrary to my own initial reaction and the suppositions of several here, the core is one piece. I fairly quickly came to this conclusion myself, even before I talked to the maker to confirm, because the split is far from uniform and because making 4 layer sandwich just doesn't make sense.

My oil MAY have been too fast, though I think it would have been perfect for the CruForge alone, and I believe that the completeness of the conversion to martensite (which is, of course, a larger molecular structure), coupled with the total lack of hardening in the wrought, essentially blew the knife apart. Using a slower oil might lessen the initial hardness, which seems like a tradeoff I'd not like to make. OF course, if that's the only alternative to a "reverse tapered tang" it might be the best way to go. The oil speed may also have been irrelevant, because this is the first time this maker of san mai has had a blade made from one of his hundreds of billets do this, and I know of several knifemakers who use his stuff in this exact combination of materials that have stated that they use Parks 50 without issue.

As others have mentioned, this core splitting has been noted to have occurred with L6 and O1 cores and non-hardening cladding, so it's a known potential issue. The question to me is not "why do san mai blades do this?," but rather "why did THIS blade do this when no others from this maker with this combination of materials have?" I still have no answer for this second question, though I feel pretty confident in the answer to the first.

Other than using more compatible materials in the first place (not an option for me at this point), solutions include heavily claying the spine and tang or edge quenching or both.

So, ultimately it appears that the only fault involved is the large one down the middle of my blade. I could have heat treated more appropriately had I known about the potential issues beforehand. The maker could have warned me, but as this had never happened to his materials before, there's no reason he would have known to. Similarly, he could have used a different combination of materials, but again, without having experienced such issues in the past there was no reason he should have done differently. From the theoretical perspective I suppose we both understand why this could happen, but neither of us considered that it might. To his great credit, the san mai maker seemed genuinely bummed that I lost what would have been a really, really nice blade, and has offered to replace the piece that was destroyed. You can't really ask for better service than that.

Randy, care to share your recipe?
 
Good shot, Travis. I'm glad to hear a good resolution to this aside from a scrapped blade - Per the photos it sure looked like a clean split right down the middle of the center.
 
Its hard for me to wrap my mind around any steel splitting under this circumstance In metallurgical terms, what takes place.

Fred
 
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Fred, I think since the cruforge expands in its martensitic state and the wrought doesn't, the internal stress, coupled with the brittleness of fully hardened but untempered steel, caused it to split. I think it split down the middle because the wrought layers are about the same thickness and the stress was thus evenly distributed, making the approximate middle the split point. The split isn't straight or precisely centered, which may not be obvious in the pictures. I am certain that it isn't an issue of a failed weld in a 2 layer core.

ANyone else have any pictures of blades that have done this?
 
At least you KNOW the welds of outside metal to center metal was solid!! This weld was strong enough to split solid metal like that. I'm impressed with the welding!

Ken H>
 
A few yeard ago, Burt Foster had a SanMai of [IIRC] 1095 & 304ss at Ashokan that was split down the spine.

It does happen. :31:
 
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