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Hey guys I recently made some sanmai 1018/1084 and all of my welds were solid and has no delamination of any sort. I went to heat treat it, thermal cycled 4 times and then quenched in mcmastercarr super quench. The blade passed the file test with flying colors. However upon further inspection there was a crack in the middle of the core steel running the length of the blade...like it just wanted to spilt in 2. What cause this and what am I doing wrong? I know people make low carbon sanmai with a high carbon core all the time. I suspected that I may have over heated it so I took it to the vice and snapped it at the tip, the middle, and at the heel. All of the grain was silky like you would find if you snapped a file so overheating is out of the question. Thanks for the help guys!

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Yep, been there.

 

In the words of Kevin Cashen

 

"It is the expansion of the hardenable steel as it is setting up that creates the issues when it is held by another steel that is not moving at all. While the austenite to martensite transformation is occurring the lattice is more susceptible to coming apart and so if the outer surfaces are held fast it own expansion tears it in half. Others have had luck with not burying as much of the insert in the iron. Leave the iron thin, the steel thick and leave more of the steel hanging out the end and see how it works. "

 

In my own experience I've found that grinding a slight bevel on the spine (think false edge along the whole spine) prior to ht totally solves the issue. Then after ht I grind the false edge back and round it over. Not ideal, but it has totally fixed the problem for me.

 

Also an interrupted quench could help solve the issue. Oh and you shouldn't be preheating your oil if you are, room temp is good.

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Thanks for the advice! Why wouldn't I preheat my oil though...I thought you were always suppose to preheat it? The next one I tried today actually did the same thing but at the edge this time

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The oil is heated to improve the rate and evenness of heat transfer. The goal of every quench is to have the slowest rate possible that still produces the desired transformation (typically we want 100% martensite, but this isn't always the case). Not heating your oil will slow the heat transfer and thus could be gentler. 1084 is pretty easy to harden, so slower should still likely work (please note I have not used that quenchant at all, let alone on 1084, so I don't know for sure).

 

I'm going to have to mildly disagree with Kevin Cashen (via the quote from N Runals) though.

 

Let's walk through the quench. As soon as the blade enters the quenchant it begins cooling from the outside in. Let's assume that the heat transfer is even (it isn't, but if everything goes well it should be close enough that we can work with the assumption). The blade start hot, and everything is austenite. Due to the thermal expansion and phase change, the blade is a bit larger in volume at the beginning than it will be at the end. Since the 1018 is on the outside, and the part is losing heat from the outside-in, the 1018 will shrink before the 1084 on both accounts (thermal expansion and phase change). The net difference between the 1018 and 1084 will be about 4% (as discussed a bit here). The thermal expansion (and contraction) should hopefully be another thing we can assume is a non-factor if everything goes ideally, where all the metal cools at the same rate. This is an assumption we cannot safely make though. The outside will definitely cool first, so the 1018 will shrink first, then the 1084 (just talking thermal expansion here). After the 1018 has pretty much finished changing, the 1084 will continue to shrink as it continues to cool. This will put stress on the 1018/1084 joint, and indeed cause strain (the engineering kind of strain --> deformation). Then the 1084 does its phase change, expanding from "cool" austenite to "cool" martensite. This puts more stress on the joint and strains it in the opposite direction. Since the first bit of strain is pulling the 1018 and 1084 apart, I would bet this is where failure is coming from. The second strain is then pushing the 1084 into the 1018, which is less likely to cause problems, except there is more movement and a problem (crack) has already started with the first bit of strain. All of the strain is leading to shear, which is definitely bad for weld joints.

 

Now, I would bet through all that (for those that read it all) you were thinking about the geometry in relation to the flat of the blade. But what about along the spine? There the 1018 and 1084 are definitely cycling at the same temperature so thermal expansion is the same right there. There we will have an expansion problem due to the phase change. It is closer to 3%, since the 1018 is already pearlite and the 1084 is still austenite (a difference in volume of about 0.85%). That is what really causes the start of the delamination. Then (to varying degrees) the above scenario plays out to further pull things apart.

 

Did you really think I was going to disagree with Kevin on this one? B)

 

If you can get stronger welds, they will withstand more stress and strain. If you can protect the spine (edge quench or clay the spine), you should reduce stresses and strains. If you quench as gently as possible (again, always the goal), then you should reduce stresses and strains. And of course, I'm sure there is even more to it than all of that too.

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The reason I say not to preheat the oil is because you are getting a violent reaction in the quench and you are trying to limit the damage. Heating the oil speeds up the quench which is good if you are quenching steels that are totally stable and homogeneous (or have a similar reaction) it helps you get the full hardness from the steel, but if the steel is destroying itself using room temp oil may be all it takes to not crack.

 

I use parks which has a similar cooling curve from 50-150 degrees. It may be different with mcmastercarr super quench I don't know.

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Very interesting guys! I meant to ask, why does putting a bevel on the spine prior to quench seem to alleviate the cracking problem? I do recall seeing a video of Stephan fowler making a Wrought and 52100 blade and when he was preparing the billet he tapered the core steel so that it had the cross section of a knife edge and put the "edge" portion where the spine would be and left the fatter portion hanging over where the edge would eventually be. I think this was partially to compensate for the higher malleability of the WI but could this also be something that will help reduce the chance of the core splitting? Last question...how do I make my welds stronger? I started with 3 even bars that were ground clean and fluxed before it started to scale...I forge welded the billet 3 times. Shouldn't these welds be strong as is or am I missing something?

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First I really don't think the welds are the problem at all. If it is what it looks like the core split and there was no delamination...

 

The spine bevel is something I made up in my head, it makes sense to me and it works for me, but I can't really explain why it works.

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I couldn't tell where the initial problem was (before the intentional breaks) and forgot that I read there was no delamination. Since the core bar split then that just means the stresses and strains mentioned earlier broke the core bar rather than the welds. Apologies for not being clearer earlier. "Stronger welds" generally refer to making sure there are no defects in the welds. But it is also possible to make them stronger by holding at high temp (or even forging more at welding temp) to get more diffusion going on. Please be aware of the grain growth issues that arise with that though. And since you didn't have delam that means you don't have to worry about improving them anyway.

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So... would normalizing help with this prior to HT?

 

-Gabriel

 

(I don't mean to butt in, I just found this all fascinating!)

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Thanks to both Nate and Jerrod for their input.
I can speak to two things here.
The first is, Jeff what were your temps for cycle and quench?
Second I use Mcmasterr 11 second oil. Is this the oil you are using.
They sell a 11 second and a 13 second oil.
There is nothing I have put in 11 second oil that does not harden BTW. All the 10xx, O1, 15n20, W series, 80crv2 and 5160.
I know its designated as 11 second but everything gets under the nose with it.

Ok back on track.
What I am curious about is how much mass of the 1018 you had on the outside.
The picture of the piece in the vice after being broken shows light and dark.
If the light is your core and the dark is your jacket there are thin and thick parts leading to problems of cooling rate that Jerrod spoke about.
From outside in.
But the in, is uneven. If you get the core steel cooling in one place before another becuase it is almost on the outside it seems to me that its going to move.
This is seems to be backed up by the picture where you show the actual crack from the top.
See how it waves back and forth.
There seem to be two possibilities. Either the crack jumped form one side of the core steel to the other.....hmmmmm, possible? Maybe.
Doesn't seem probably to me.
So if its not jumping from side to side what we are seeing is the core steel has either warped into a snake, a reason that there could be weld shear from the violence of the quench alone. Or the piece is unevenly forged.
When you do San Mai or other jacketed methods its important to keep the core as straight as possible and the jacket an even thickness on both sides.
This is helps prevent warping among other things.
If you leave the jacket thicker and the quench does not get all of the steel under the nose and make martensite it only really needs to harden a portion of the edge up to maybe 1/2"
We have to remember why steel is jacketed.
1: Conservation of material.

2: Toughness of spine that allows flex.
Thus if the core steel towards the spine doesn't harden, no big deal really the edge is what counts.

3: looks.
The weld line looks nice especially in contrasting material.

I'm very interested in everyones ideas on this.

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I had same problems with Japanese triple layer steel-core layer from Hitachi white paper steel (via Dictum store)

Outer layer of not hardenable very low carbon steel....

 

I quenched the first in brine edge first,it cracked in the middle of the core steel running the length of the blade.

Next blade quenched from non magnetic to preheated canola edge first,same problem...

 

The third blade it was the very same in all (grinds-shape all the same with previous)

This third time i quenched the blade from non magnetic to brine spine first....and success!!!

No warp no delam no cracks in the middle of the core steel!And crazy hard !

 

That method worked for me!

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When I was using 1095 for axe bits and water quenching them I ran into this. Switched to mineral oil and it hasn't happened since. This suggests to me the quench may be too fast for the reasons Jerrod outlined above? Nate is headed that way with the room temperature oil instead of warm oil. At any rate, as annoying as it is to have the steel split, it's a pretty cool phenomenon!

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I had this very same thing happen to me. However I was following the advise of an ABS mastersmith in the set up I was using. He told me about being able to build a san-mai of low carbon and 52100 and quench in warm water. Now he had told me he has been doing this for years and has had great results. So I jumped in with both feet. I built a billet of 203E and 52100. Welded up everything, hammred it out to a very thin, .080", and then annealed it. Normalized a couple times and let it sit for a day. Profiled out the blade and into the HT oven and ramped up to temp. Pulled it and quenched. I guess the universe wanted everything to work perfectly cause to my absolute wonder everything came out great. No cracking, no warping and it was perfect. So I tempered it and ground it. One of the most beautiful kitchen blades I have ever done.

 

So with this under my belt I made 6 more billets, Shaped out 6 more blades and HTed them just the very same as the first one. However, all 6 cracked and failed the quench. I had one of them that split nearly 1.5" at the tip before the steel quit moving. I was crushed. At this point I had almost 8 hours in this set of 6.

 

After learning that, I am only going to use my Parks 50 for pretty much everything. Well that is unless it is just a fun experiment I am working on and don't mind losing the blade.

 

Guess you can't believe everything you are told by mastersmiths, lol.

 

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Edited by jo_smith
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I've only made a handful of san-mai blades, but I've been bit by this too. My solution was to edge-quench about half the blade width, so far I've not had this problem again using this method.

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Those are some absolutely beautiful blades! Thanks a lot guys I'm eager to try out some of the suggestions! I have one in the works now so let's hope for the best and I'll keep you posted!

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I was going to suggest edge quenching. It seems to help a lot with the internal stress leading to the tearing of the core. I'm hoping Daniel Cauble will jump in on this thread, he has an incredible example of what happened to you all. In short, large knife split entirely in two, dead centre down the core. No warping other than the peeling outward from the failure, and the low carbon cladding was very consistent on both halves. Great grain too from what I remember. I'd be very interested to figure out what's happening from a metallurgical chemistry perspective, but can't quite find anything definitive enough to explain it. All accounts suggest that it has nothing to do with the weld lines or possible flaws, so I wonder if it is possible for this to happen with a bar that began as homogeneous and had the carbon leeched from the outer surfaces. Curious...

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I was going to suggest edge quenching. It seems to help a lot with the internal stress leading to the tearing of the core. I'm hoping Daniel Cauble will jump in on this thread, he has an incredible example of what happened to you all. In short, large knife split entirely in two, dead centre down the core. No warping other than the peeling outward from the failure, and the low carbon cladding was very consistent on both halves. Great grain too from what I remember. I'd be very interested to figure out what's happening from a metallurgical chemistry perspective, but can't quite find anything definitive enough to explain it. All accounts suggest that it has nothing to do with the weld lines or possible flaws, so I wonder if it is possible for this to happen with a bar that began as homogeneous and had the carbon leeched from the outer surfaces. Curious...

 

It is just an expansion contraction issue with stresses that are too high for the brittle hardened core. I feel pretty safe saying that with some certainty. Diffusion won't play enough into it to really be noticible.

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The only reason I would make san-mai is to be able to totally harden the blade so the steel inside would be able to be sharpened through the life of the knife. Edge quenching san-mai seems to be a bit pointless to me. The only reason I say that is because if you were to edge quench the center steel itself you would not need to weld a billet in the first place.

 

I know that grinding the blade and etching it looks very cool, but when it comes to performance the reason for making san-mai is to have a much harder and more brittle center steel that will cut and flex beyond what it would if it was not clad.

 

Those are only my thoughts and I don't want to upset anyone at all. I tend to look at the over all performance of what I am trying to make vs how it looks. Meaning I tend to make some really ugly blades, lol.

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I understand where you are coming from Jo and I agree. I'm going to continue to experiment with this and ditch the clay and see if room temperature oil will do the trick by itself.

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Here's a picture of the current cruforge and 1018 gyuto currently at 60 grit. I was hoping the core would've been closer to the edge but I think if I forge the blade thinner next time that problem should be alleviated.

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If the purpose behind san-mai is to have an ultra hard core, it should be noted that if the blade is not tempered back sufficiently the edge will still chip. I use primarily shallow hardening steels, so it matters little if the entire blade is quenched, I'm still not going to get full hardness all the way through the blade... the edge-quench is entirely to avoid the blade being ripped apart, in this case it serves no other purpose. With a deep hardening steel like cru-forge I think the slower quenchant would be a better solution.

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