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blades cracking, weird stuff is happening again...


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So I started my blades with a san-mai billet, regular hardware store low carbon steel, I'd been using for ages, never had a problem.
chiseled the bar and put a file steel core into it, that I had put through some tests beforehand,
I forge welded it all into one nice solid piece, then cut it in the middle and forged in the tips of the two small knives and closed shop for the day.

now at this point the steel was all good, clean, solid, no cracks!
 

today I went to refine the knife blanks and after a few blows I notice that the low carbon steel has micro cracks all over, like a ton!
I was forging at a middle orange heat.

after that it was time to experiment, I tried to go for different heats and even hot rasped all the cracks off but they came back.

now the only thing I could think of is, voodoo, that or maybe something happened to the cold steel when I put it into the forge for the first time?
I had the forge already blasting hot for some warm up forge welding. 
so could it be that somehow the low carbon steel was destroyed because it shot up in heat too fast?
(im using charcoal btw)

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I don't know what they sell in Germany, but around me, the stuff in the hardware store is highly variable in terms of its chemistry..  If it is a new bar, it may have some strange chemistry that isn't compatible with the file steel core.

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yea I had forged some other san-mai knives from the same bar I even had used the same file steel before.
only difference was that I forged one billet and cut it into 2 knives. 

 

27 minutes ago, Brian Dougherty said:

I don't know what they sell in Germany, but around me, the stuff in the hardware store is highly variable in terms of its chemistry..  If it is a new bar, it may have some strange chemistry that isn't compatible with the file steel core.

not "compatible?" in what way? 
the carbon core seemed fine, 

the cracks were everywhere except at the spot where the core was.
they traveled right around the spine over the faces and then stopped in the middle right at the edges of the welded core as far as I could tell.
 

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7 minutes ago, J.Leon_Szesny said:

not "compatible?" in what way? 

 

That is probably better answered by one of the folks with more metallurgical knowledge.  I know some allowing agents, and some contaminates, that end up in recycled steel that is sold in hardware stores can cause welding issues, and issues with the steel moving at different rates than what you weld it to.  This can lead to cracking and delamination.

 

However, this probably isn't your issues if you have used some of the same bar in a similar project before.

 

 

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Can you post a picture of the cracks?  It would be interesting to see if it is intergranular or transgranular.  My best guess is that the mild steel is just not that good of a material.  This is mostly likely to happen with inconsistent chemistries (even in the same bar sometimes) combined with inappropriate heat treat (which could be exacerbated by the bad chemistry).  In a nutshell, I would guess the grains grew too much, but even more so the grain boundaries got too much stuff caught in them.  Very hard to fix too much junk at the grain boundaries, unlike fixing enlarged grains.  Just my best guess at the moment.  

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true, the carbon steel core seems to be perfectly fine and I also saw no de-lamination at all
but that sounds interesting, I hadn't heard of that before.
 

maybe while forging and making knives and cutting the bar down, I just hit a specific part of the bar were something funky was going on.
If so, any ideas on how I could test for things like that?
cause I did forge it down, chisel it, straightened the slot, chisel it open again and nothing happened to the steel, I was doing that at orange heats and working even down at red heats.

 

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1 minute ago, Jerrod Miller said:

Can you post a picture of the cracks?  It would be interesting to see if it is intergranular or transgranular.  My best guess is that the mild steel is just not that good of a material.  This is mostly likely to happen with inconsistent chemistries (even in the same bar sometimes) combined with inappropriate heat treat (which could be exacerbated by the bad chemistry).  In a nutshell, I would guess the grains grew too much, but even more so the grain boundaries got too much stuff caught in them.  Very hard to fix too much junk at the grain boundaries, unlike fixing enlarged grains.  Just my best guess at the moment.  



here that's the best I can do rn, bad lighting and because I was kinda disshearted...I didn't bother to clean them up with water forging, I just got them to that rough shape and chucked them in the ash for annealing.

IMG_20201015_230029.jpg

IMG_20201015_230001.jpg

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wait what, thermal cycles after forge welding?
I mean, I forge welded it into a solid billet then took it to slightly below welding heat and hot cut it in the middle, both halves I then heated to cherry red and just let them air cool....

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I wouldn't know if I call it stress, the billets look pretty straight! I know I've left steel in the heat too long way back when and it looked a lot like that. The metal went past some temp point and started to break down. It was mild steel as well. If I were you, I'd stop using the batch you have. Do you have any sawmills around you? If you do, go see the foreman about any broken bandsaw blades they might be ready to scrap, that and high carbon steel should give you a better shot at making a nice san mai until you find a new source of mild steel to use.

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21 hours ago, Brian Myers said:

I wouldn't know if I call it stress, the billets look pretty straight! I know I've left steel in the heat too long way back when and it looked a lot like that. The metal went past some temp point and started to break down. It was mild steel as well. If I were you, I'd stop using the batch you have. Do you have any sawmills around you? If you do, go see the foreman about any broken bandsaw blades they might be ready to scrap, that and high carbon steel should give you a better shot at making a nice san mai until you find a new source of mild steel to use.


yea maybe it was a bad section in the bar... I'll try to test the remaining steel, maybe I can find something out

not sure I understand this, are you talking about making a san-mai billet with nothing but high carbon steel pieces?
but that would kinda defeat the purpose of the san-mai lamination technique

but no, no sawmills, we do have a local scrapyard with piles of circular saw blades

 

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15 hours ago, J.Leon_Szesny said:

but that would kinda defeat the purpose of the san-mai lamination technique

 

Which you don't really need for strength with non-tamahagane steels, just for looks.  And you're doing more kobuse than san mai construction anyway. ;)

 

In all seriousness, though, the circular saw blades are probably a tough but not particularly hardenable steel provided they have inset or brazed-on teeth.  Certainly better quality than hardware store mild.  

 

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5 hours ago, Alan Longmire said:

 

Which you don't really need for strength with non-tamahagane steels, just for looks.  And you're doing more kobuse than san mai construction anyway. ;)

 

In all seriousness, though, the circular saw blades are probably a tough but not particularly hardenable steel provided they have inset or brazed-on teeth.  Certainly better quality than hardware store mild.  

 

I had read that one of the purposes of having mild carbon steel and a paper thin core was to help reduce sharpening time?
most of the circular sawblades around here are highly hardenable even the ones with brazed on carbide!
and I had some weird welding times with some, so I've been avoiding it...I think it was chrome vanadium and some kinda HSS.

 

 

56 minutes ago, John N said:

probably just too much air blast in the solid fuel forge, and you de-carbed the outer layers of the san-mai. 

yo, that could perhaps be, I was operating my fuigo bellow with my foot on the footrest so, maybe I pumped too much air into it?
but I didn't get the steel sparking hot, could it still de-carb? 

here some pictures of the blades a bit cleaner, maybe the cracks will ring some bells with someone?
I think I can still make working knives out of these since the core is untouched buuuut....?
 

IMG_20201017_115931.jpg

IMG_20201017_115940.jpg

IMG_20201017_120002.jpg

IMG_20201017_123658.jpg

IMG_20201017_123716.jpg

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Jep I´ve burned plenty of steel, and it looks just like that.

 

By any chance, are you using the japanese style of welding where sparks are flying everywhere? I did exactly the smae when I was first learning forge welding.

It works for the bloomery steel the japanese are using, but modern mild steel will just desintegrate at those heats.

 

If I were you I would look around for some wrought iron, this will work better with traditional methods and also look nicer in the finished product.

Angele in germany also sells very pure iron, which is nice and reliable for san-mai, and more like what they use in japan.

 

https://www.angele-shop.com/shop/de/schmieden/schmiederohstoffe/reineisen/

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1 hour ago, Alan Longmire said:

That really looks burnt to me.  

Really you recon it's burnt!?

I swear that I welded and forged it without sparks flying!

But maybe the heat shot up too fast, which caused the steel too be more stressed?

When I started refining the blanks the forge was already at forge welding temp.

 

13 minutes ago, Pieter-Paul Derks said:

Angele in germany also sells very pure iron, which is nice and reliable for san-mai, and more like what they use in japan.

 

https://www.angele-shop.com/shop/de/schmieden/schmiederohstoffe/reineisen/

Wrought iron would be a dream to have, l source most of my stuff locally, sadly haven't come across wrought iron yet...

But the option on website seems surprisingly affordable! Really I thought it be 3x as much.

 

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