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Noah M Legel

My First Sanmai, a Blacksmith's Knife

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So, I have gotten to start playing with some methods that are outside my wheelhouse, lately, thanks to a new forge showing up under the Christmas tree. Initially, I just stuck a piece of O1 to a piece of mild, to see if I could, and it stuck really well, so I tried to make a little Sanmai sandwich of mild and 1095. That billet seemed to be pretty solid, so I figured I might as well make a test knife out of it, and see how it goes. I banged out a super simple drop-point blacksmith's knife and sanded it up to 330 grit before hitting it with some polishing paste and giving it a ferric chloride bath to see how it turned out. Overall, for my first ever attempt at a forge-welded blade, I would say it went pretty well. I'm guessing some carbon migration was going on to cause that dark cloudiness along the transition line? That, or maybe I just ground down too far?

 

The only thing that really went wrong was a lovely *ting* in the quench--a hairline crack down the center of the spine. Surprisingly, in the middle of the 1095, not along a weld. To be fair, I was quenching in vegetable oil, not a proper quenching oil, but it's worked well for 1095, 5160, and O1 before now. Still, even with the crack, my girlfriend is going to use it around the house for light duty, so it shouldn't be a huge issue for that.

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Noah!  Welcome back, man!  How's the leather business going?

 

As for the crack, yeah, 1095 and mild san mai will do that almost every time in a fast oil or water.  Nice lines on that, btw.

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2 hours ago, Alan Longmire said:

Noah!  Welcome back, man!  How's the leather business going?

 

As for the crack, yeah, 1095 and mild san mai will do that almost every time in a fast oil or water.  Nice lines on that, btw.

Thanks! Honestly, doing it as a business kind of killed the fun in it for me, so now I just do it for friends and repeat customers  :P. Good to know on the cracking--can I heat the oil more to prevent that, or do I just need a different quenchant?

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I'd try the oil not quite as hot, say 70 degrees. It gets faster as it gets hotter.  

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On 1/22/2020 at 6:33 AM, Alan Longmire said:

I'd try the oil not quite as hot, say 70 degrees. It gets faster as it gets hotter.  

Ah, right! Viscosity and whatnot--I completely forgot! Just quenching monosteel blades for a few years, now, I've just done what Tai Goo showed me and preheated the stuff. Makes sense, though. Thanks!

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The funny thing is, it's the mild steel that causes the issue.  If that had been plain 1095 it would've been fine.  It's the same phenomenon that causes the curve in a katana, the unhardened back pulls the edge up while it's still hot enough to move, but not cool enough for full martensite conversion.  The blade nosedives, then slowly curves back up.  With san mai it can't do that since there's unhardened on both sides.  If the core steel gets fully hard before the cladding shrinks, it has no choice but to tear down the middle.  

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22 hours ago, Alan Longmire said:

The funny thing is, it's the mild steel that causes the issue.  If that had been plain 1095 it would've been fine.  It's the same phenomenon that causes the curve in a katana, the unhardened back pulls the edge up while it's still hot enough to move, but not cool enough for full martensite conversion.  The blade nosedives, then slowly curves back up.  With san mai it can't do that since there's unhardened on both sides.  If the core steel gets fully hard before the cladding shrinks, it has no choice but to tear down the middle.  

 

Yeah, when you mentioned it happened because the oil was fast, that's kind of what I figured. I wonder how it would do with a full jacket, forge welded taco/hotdog bun style? On the plus side, the fact that the welds held up under that pressure is a good sign? I'm curious to play with it in cooler oil, now, just to see, but I also want to try doing some proper 1095/15N20 "Damascus," next. I'm the type to try and jump into the deep end and do things that are more difficult/complicated than I really should be attempting, so it was hard enough doing Sanmai when I really wanted to go straight to a 1095/15N20 twist, lol.

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With the hot-dog-inna-bun weld it'd just give it some curve, possibly in the wrong direction...  Go for the damascus, it's actually easier!  B)

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