Help me wrap my head around this, please

Bühlmann

Bühlmann

North Lake Forge
Joined
Jan 6, 2022
Messages
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This may be a very basic question but I'm not finding the answer I'm looking for. I'm not questioning the truth of it, but I'm more looking to know "why" it is the way it is.

How does a laminated blade, like san mai, make a blade tougher? Here's an analogy that is hanging me up....san mai is like placing a cracker (HC steel) in between two pieces of cheese (mild steel). If you bend the sandwich, the cracker will still snap in between the cheese. So why wouldn't the same happen in a san mai blade?
 
The way it was explained to me is that you can have a thinner core of hardened steel since you have milder steel cladding supporting it. Thinner means more flexible, so a san mai blade in theory would be less brittle than a blade made of mono steel.
I'm sure others can explain it better than I can! :)
 
I am also not sure, but I'll give my opinion.

The San Mai construction allows you to put pretty thin high hardness core and still have normal thickness blade. So the very thin core can bend without breaking (you know even glass can bend if it's thin enough) And the outer jacket will provide strength to the whole construction. If it's soft steel - it will bend and can be straightened, if it's springy it will return back to straight on its own.

If the outer layers are very thin and the core is thick it will happen what you predicted - the core will just break. But that's not the proper San Mai construction (at least for functional purposes, maybe just for aesthetics)

Sorry if my explanation is unclear my English is not the best.
 
Remember that when you bend something the outside changes more than the inside. for any bend there is a line in the inside where the length does not change. When a crack starts its going to be on the outside, because that's where the compressive or tension forces are
so that's why the inner hardened part wants to be thin.
instead of a cracker think of a piece of rice paper between the cheese.
 
In its original use, san-mai was a method of making a very sharp and hard edged sword that could withstand damage that would cause a fatal flaw in a mono-steel blade.
Scenario A:
A mono-steel blade gets bent sideways in a deflected blow or gets struck straight into the edge by another sword. Either case will have a good chance of making the blade crack and then break in two pieces. This is a fatal flaw and would likely lead to death from the opponent.
Scenario B:
A san-main sword receives the same blow that caused the mono-steel blade to fail. The soft cladding does not break. Even if the core breaks all the way through, which is less likely but possible, the cladding will, keep the sword in one piece allowing continued attack or defense.

An additional advantage was easily straightening a bent sword in battle without as much risk of it breaking.

The same issues apply to shorter san-mai blades in preventing breakage in field use. A broken knife can be life threatening in a person out in the wild. Nordic and Saami fishing and hunting knives have been laminated for a very long time, probably over 1000 years.
 
Stacy, that's an awesome real-life explanation. It also makes me wonder about a lot of the "san mai" you see out there. A lot of times the steels used are 1084 and 15n20. Seems to me that defeats the purpose - you're using two high carbon steels that will (with etching) give you some nice contrast, but you're not making a blade that has the functional advantages of having that soft cladding around a hard core. I think I'm going to work on some knives that are more traditional san mai.

Do you have suggestions on steels to use?
 
Dimitar Popov said:
my English is not the best.
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From what I've seen in your posts, your English and explanations are as good or better than most who post.

dwaterfield said:
Do you have suggestions on steels to use?
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Well, since you're wanting the traditional approach, I'd think a 1018 mild steel would be used for the cladding. I personally like 26C3 for the core.
 
From what I understand it was a way to use scarce and expensive hardable steel in an economical way
 
dwaterfield said:
Stacy, that's an awesome real-life explanation. It also makes me wonder about a lot of the "san mai" you see out there. A lot of times the steels used are 1084 and 15n20. Seems to me that defeats the purpose - you're using two high carbon steels that will (with etching) give you some nice contrast, but you're not making a blade that has the functional advantages of having that soft cladding around a hard core. I think I'm going to work on some knives that are more traditional san mai.

Do you have suggestions on steels to use?
Click to expand...
I think most san mai today is made for looks, and maybe a tip o' the hat to the Old Ways of traditional craftmanship. That's not to say that there isn't a benefit to using two HC steels with different properties, or even better using a stainless cladding over a HC core.
 
I agree that modern san-mai is for looks. Often it has damascus sides and a very hard core like VG-10 or Elmax. Damascus sided san-mai is called suminagashi. Historic san-mai had plain iron or even wrought iron sides.

In Japanese sword making the cladding was made from all sorts of scrap and the Hocho (low carbon parts of a bloom) after the orishigane (good blade steel) has been removed. These were folded many times, just like the blade steel. By using soft iron scrap they made a low carbon steel. The folding made it homogenous, and also created a sort of hada. Since this was much ess valuable than the scarce tamahagane orishigane (hardenable tartara steel), it was perfect for san-mai. A well-made Japanese san-mai blade may rival a forged bade with a hamon ... or at least come close.

The modern standard of 15N20 and 1084 is common because they weld together easily and show a good contrast when etched.
 
Thanks everyone for the responses about steel. I'll have to think about what direction I want to go. I've seen some folks online that are doing wrought iron plus a hard steel....not sure that I have a source for wrought iron though!
I may start with the modern approach just to improve my forge-welding. I've read a lot today about the difficulties of welding a soft steel that wants to move to a hard steel that doesn't.

EDIT: I did just find a company that claims to be a supplier of real wrought iron, made from old mooring chains. Might give them a try.
 
dwaterfield said:
Stacy, that's an awesome real-life explanation. It also makes me wonder about a lot of the "san mai" you see out there. A lot of times the steels used are 1084 and 15n20. Seems to me that defeats the purpose - you're using two high carbon steels that will (with etching) give you some nice contrast, but you're not making a blade that has the functional advantages of having that soft cladding around a hard core. I think I'm going to work on some knives that are more traditional san mai.
Click to expand...
My understanding this was the case for pattern welded steel too. The techniques were developed to deal with poor quality steel, but now they are used because it looks cool.
Which if you think about it is a nice benefit of improved tech, we get to focus on aesthetics rather than if it works in the first place
 
For simple san-mai on a budget you can use plain welding steel from the hardware store (or anyplace) and a hardenable core like 1084. It will look very much like a traditional Japanese blade. A36 welding steel is basically 1018.
 
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