"Ultimate" san mai - speculative fun

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RX-79G

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Jun 23, 2006
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So the whole idea for laminates is to have a good edge steel do the edge thing, and something "tough" (whether that means very plastic or actually tough) on the sides. What would you make as an "ideal" laminate to make a blade that has an amazing edge but tough overall?

The complications are:

Not every steel is going to forge at overlapping temperature ranges, or be able to be reasonably heat treated together. (Not much point in using some super steel for the sides if you can't at least austenize it to get those properties.)


The other "big" issue is carbon migration. If your outer layers have .6% carbon and your core is S110V with 2.8 carbon, but the time you get done the core is going to down below 1% and your sides are going to be hypereutectic. I've heard it suggested that a layer of nickel may stop migration, but at a strength cost. I don't know if there is another type of construction that can limit the diffusion (like an edge to edge rather than sandwich), but I doubt it. So using steels with similar carbon levels to limit the amount of migration might make the most sense.

So while S90V with S7 might be attractive, 3V with with S7 might be a good combination if you heat treat at the higher temp for wear resistance.



Not trying to reinvent the wheel - monosteels work great, as do more normal laminates. Just thought the topic would be interesting. Thanks.
 
By personal experience, one does not need to austenize stainless on the sides for it to be tough. Even at forging temps, it just flat does not want to move.
I had an issue with one once and used it for experimenting.
Even in the unhardened state - other than the bottom working portion - it took everything I could personally do to get a .250" blade to budge.
I hate to use the word indestructible, but there was nothing I could do in my power to destroy that blade.
I was impressed.

1095 core/410 jacket.



 
And the carbon migration is not anywhere near your speculation.
Carbon only migates in micron measurements over HOURS at welding heat.
The reason we get such carbon migration in high layer Damascus is because we reduce the layers to miniscule thickness, thus reducing the distance of "travel" for the carbon to equalize.
My layers are 3/8" thick 1095 core and 1/4" thick jacket.
I only spend about 1 hour gradually working down the knife to about .300" thick before I go to the surface grinder.
The core carbon % for the most part is unchanged from its original condition.
It's still 1% carbon.
The only migration is right at the interface of the layers - and that is only what can be seen there in that raw iron layer where it lost its carbon. (The shiny layer).
 
Karl B. Andersen said:
And the carbon migration is not anywhere near your speculation.
Carbon only migates in micron measurements over HOURS at welding heat.
The reason we get such carbon migration in high layer Damascus is because we reduce the layers to miniscule thickness, thus reducing the distance of "travel" for the carbon to equalize.
My layers are 3/8" thick 1095 core and 1/4" thick jacket.
I only spend about 1 hour gradually working down the knife to about .300" thick before I go to the surface grinder.
The core carbon % for the most part is unchanged from its original condition.
It's still 1% carbon.
The only migration is right at the interface of the layers - and that is only what can be seen there in that raw iron layer where it lost its carbon. (The shiny layer).
Click to expand...

Interesting. The information I had gotten from Kevin Cashen's site was that carbon was extremely mobile, and even austenizing cycles allows the carbon to move around substantially. I guess it would be nice to find a rate.

I would think the thickness of the center layer would have a huge impact since it shares so much surface area with the cladding. The difference in concentration probably also matters. But maybe the issue overall isn't that big a deal.
 
Yes - carbon is very mobile and fluid, even "substantially" - at the ATOMIC LEVEL.
Not at the level where it could be measured in thousandths of an inch in an hour's forging time.
Kevin has examined my San Mai and described to me what's going on in the different layers that can be seen in the photos above, but that carbon-loss area shown in the shiny part is so thin as to be immeasurable except with instruments that I certainly don't possess.
There is a full 1% carbon on that cutting edge up there, and even outside of that - just like the steel began with.
 
RX-79G said:
If the carbon thing isn't a problem, I could see trying S7 and CPM M4!
Click to expand...

Carbon is not the only problem.
Early on, before I figured out what I was doing - and I know this has happened to others as well - I had blades split in two - right down the center, like pulling a sandwich apart by separating the slices of bread - because the core had austenized and when making its transformation to martensite, its stresses were inhibited by the non-moving jacket.
A stainless jacket will remain basically motionless at the temps used for hardening simple carbon - but the simple carbon wants to move.
The stainless wins. It's tough.
And that split has nothing to do with carbon - but rather alloy like chromium.
So, there are serious issues when making san mai.
They just need to be accounted for.
 
Somebody mentioned an idea of making San Mai out of cold steel blades. I like that a lot.
 
There are people who do CPM-154 and S90V core and CPM-154 and M4 core. These two steel has very similar heat treat.

The purpose of making laminated steel today is for aesthetic not for performance though. We already have too many high performance mono steel.
 
I have two bars of Damascus San Mai from Chad Nichols...waiting for special projects. One is Boomerang Damascus (stainless) with CTS-XHP core and the other is Boomerang with CTS-204P core. I wholly agree that for the most part San Mai is used today for aesthetics....but not always. A carbon core with stainless cladding provides a measure of corrosion protection. As far as 154/s90V I think that combination was chosen more for the possible finish one can apply to the CPM-154 vice the S90V.
 
About a year ago I learned "ultrasonic welding" of metal was possible. The company showing off their work at a trade show had slabs with layers of titanium, carbon steel, stainless steel, brass, copper, aluminium, etc. All different thicknesses, randomly layered. They had slices of the welded material bent to 90 degrees with the joints in shear and tension and no signs of breakage or delamination.

It got me to thinking about titanium knives and the complaint that they don't hold an edge well. How about a titanium knife with a stellite core? Or if you just want light, and don't care about non-magnetic, how about titanium with an S110V core? Or even aluminium with a steel core? Or how about mokume with a steel core? Mokume that incorporates aluminium? For the person with sufficient money, a gold knife with a steel or stellite core. Lots of possibilities, but I don't know how the process might affect heat treat. If you have to heat treat after welding, that would rule out all the cladding materials that melt at lower than the critical temperature of steel. If the temperature the materials gets to during welding stays reasonable, and there is no too much disruption of the steel structure, it should be possible to start with heat treated core material. In any event, stellite cored knives of any material should not be a problem.

You'd have to take reasonable care of the knife, galvanic corrosion would be a possibility depending on the combination of materials used. Maybe if I win the lottery, I'll get some material welded up and make some knives out of it. If anyone gets inspired to start producing knives with this technology, and you heard it here first, don't forget to send me one...
 
Mahoney said:
About a year ago I learned "ultrasonic welding" of metal was possible. The company showing off their work at a trade show had slabs with layers of titanium, carbon steel, stainless steel, brass, copper, aluminium, etc. All different thicknesses, randomly layered. They had slices of the welded material bent to 90 degrees with the joints in shear and tension and no signs of breakage or delamination.

It got me to thinking about titanium knives and the complaint that they don't hold an edge well. How about a titanium knife with a stellite core? Or if you just want light, and don't care about non-magnetic, how about titanium with an S110V core? Or even aluminium with a steel core? Or how about mokume with a steel core? Mokume that incorporates aluminium? For the person with sufficient money, a gold knife with a steel or stellite core. Lots of possibilities, but I don't know how the process might affect heat treat. If you have to heat treat after welding, that would rule out all the cladding materials that melt at lower than the critical temperature of steel. If the temperature the materials gets to during welding stays reasonable, and there is no too much disruption of the steel structure, it should be possible to start with heat treated core material. In any event, stellite cored knives of any material should not be a problem.

You'd have to take reasonable care of the knife, galvanic corrosion would be a possibility depending on the combination of materials used. Maybe if I win the lottery, I'll get some material welded up and make some knives out of it. If anyone gets inspired to start producing knives with this technology, and you heard it here first, don't forget to send me one...
Click to expand...

That's pretty fantastic. Previously, the only ways to weld ti to steel was through forge welding or explosive welding.

Do you recall what company was demonstrating this?
 
Who says the outer layers even have to be steel? CF and G10 are pretty tough, and certainly very corrosion-resistant... there are likely other non-ferrous materials I don't even know about that might bear looking into.

For that matter, who says even the inner core has to be steel? Several folks produce titanium blades with carbidized edges.

Such a billet certainly wouldn't look as beautiful as true/traditional san mai, and I imagine preventing it from delaminating could be problematic. But if you could get it to hold up, it would certainly be interesting.
 
I believe there are some carbon fiber/steel san mai knives out there. I think the main problem with any sort of odd composite is whether you actually get anything for your trouble (aside from cool). In the case of carbon fiber, CF is not a very stiff or strong material in thin, flat sections. If it was allowed to flex much it is going to delaminate from shear. If you make it thick you've just built a thick chopper that is too light chop. As an aesthetic treatment some people will really dig it, but I think it is actually less functional than any steel san mai.


What I was thinking of initially is putting a very thin core of something like CPM 10V (super edge holder) between a shock steel like 1V. If the core is thin enough, the 1V's toughness should support the 10V edge against chipping and the blade overall will act like 1V. I had just assumed that after all the forging and HT, the 2.8% carbon in the core would have made it's way elsewhere. I think with a thin enough core this would still be a problem. But if you could do it, you may be able to put out a final product with edgeholding AND toughness that exceeds any monosteel. Which isn't magic - we use composites al the time because of the ability to combine properties.

4v/3v or M4/3v might be more practical combinations with less radical carbon concentration differences. I don't really know the non-Crucible offerings to jump to other brands of high end steels.


Titanium side plates could work very well because titanium acts a bit like tough steels in terms of toughness and rigidity, and it is an actual weld to the steel. So it would come out behaving much like a steel blade, just lighter. Aluminum couldn't take steel HT temps, so you'd have to figure out whether the ultrasonic welding process would damage the HT to the edge that would have to happen before welding.
 
james terrio said:
Who says the outer layers even have to be steel? CF and G10 are pretty tough, and certainly very corrosion-resistant... there are likely other non-ferrous materials I don't even know about that might bear looking into.

For that matter, who says even the inner core has to be steel? Several folks produce titanium blades with carbidized edges.

Such a billet certainly wouldn't look as beautiful as true/traditional san mai, and I imagine preventing it from delaminating could be problematic. But if you could get it to hold up, it would certainly be interesting.
Click to expand...

"Swartz Tactical" was or is a member here and does this. If I had to watch every ounce I carried I would appreciate them quite a bit.
 
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