Cladding line

[Jacob_x]

On all my san mai knives, where the cladding meets the core, is a normal, clean boundary, which when polished exaggerates the difference between the two. Normal and fine and whatever.
Now, on my Heiji, it's a little different, and I'm not sure why...
There is the tonal difference, as expected, between the more mirrored and shiny iwasaki core, and the darker cloudier cladding. But there is also a physical 'line', as if someone has drawn with a super fine pencil this boundary on the knife. This alone poses a question why on some knives there is this 'line' and on some just a smooth boundary. But here it gets more confusing to me, as this 'line' on my heiji, is about 1mm below the 'tonal' cladding line - so for 1mm above this line, it is still mirror and shiny, before you hit the kasumi cladding.
I've had this knife for about a year and always wondered, but never asked...


I know this thread is completely and utterly, annoyingly useless without pics, but I just can't capture it on my ****** phone, will try and get some pics up later if I can. But someone probably knows what I'm on about without them, maybe.

 

[khashy]

Hmm, here is a Heiji fresh out of the oven. Can you see the line you are referring to in this photo?

 

[foody518]

Like the knife on the bottom in this pic?

 

[Jacob_x]

Can't really see it on yours khashy (congrats btw, she's a cracking knife, i've had my ups and downs, but so much personality, and outrageous steel).
Yeah, kinda like on the bottom knife on yours foody, but fainter. Looks like the same thing going on though, as there is an area above this line, that is still taking the polish of the core steel, rather than the cloudy kasumi of the cladding.

Robin has suggested, as was my inital hypothesis, that there is some carbon migration going on, and so this pencil line is where the 2 steels are clad together, and the small amount of carbon that has migrated into the cladding explains for the shiny, mirror effect on the cladding steel.

Still can't get in on camera...

 

[foody518]

Jacob, is yours stainless clad semi-stainless?

Took a quick online and see photos of Masashi SLD knives showing a similar look

 

[Unstoppabo]

Maybe the flux?

 

[DevinT]

One of three things here, sometimes a thin layer of nickel is used between the core and cladding to slow carbon migration. Without the nickel, carbon or alloy can migrate causing a line to show, and sometimes during the forging process, decarb can develope on the core material and show up as a line on the finished knife.

Hoss

 

[RDalman]

On carbon a fecl etch will show it well. This is one I did recently with mild clad. You can see it in the cladding as cloudiness, I believe I felt it was harder when adding the mid hollow section and that helped me not blow through the cladding but just be close.

https://www.instagram.com/p/BTbhLqnFSeM/

Hope this is not overstepping anything.

 

[Jacob_x]

Thanks for the replies folks. Still trying to get a decent photo of it but been a bit hectic at work.
It doesn't really look like that photo Robin, and im pretty sure there's no nickel layer either.

 

[rogue108]

Why not ask Jon what his opinion is? I had an different issue where the stainless cladding on my Kochi showed an odd line where the cladding met the core steel. He had me send it in, inspected it, decided it could be fixed, made the repair, and returned it to me. I only paid shipping and wasn't the original owner of the knife. If there is a problem Jon will get you straighten out.

 

[Badgertooth]

Got out the macro as I noticed the same on my Watanabe which, I think, is stainless clad

 

[Jacob_x]

Thats the best I can get. But you can see that the line doesn't quite match up with the different polishing effect, so yeah, sounds like small level carbon migration or some such...
Thanks again for the responses

 

[refcast]

I have this in my carbon heiji, too.

I thing the dark line is the real cladding line, and the boundary is between hardened steel (bright) and soft steel (dark). There was carbon migration, so that's why the line doesn't match up with the boundary. Why there is a dark line, I'm guessing it's cause of low temperature forge welding, maybe. It's something that is physically dark . . . and I'm guessing maybe some iron oxide type thing, but the weld seems secure.

 

[Dan P.]

And the black pencil line suggests to me that the smith welded that himself, rather than using prelaminate.

 

[Dan P.]

One of three things here, sometimes a thin layer of nickel is used between the core and cladding to slow carbon migration. Without the nickel, carbon or alloy can migrate causing a line to show, and sometimes during the forging process, decarb can develope on the core material and show up as a line on the finished knife.

Hoss

There was an interesting thread on nickel on another forum;

https://www.bladesmithsforum.com/in...ckel-carbon-stop/&tab=comments#comment-368609

An incidence where nickel does not seem to have made much difference, and this knife was not held at high temps for long periods of time. I am very much "wham bam thank ye maam" when it comes to forging;

https://www.instagram.com/p/Bk9svKTgSCG/?utm_source=ig_web_button_share_sheet

I see it even more pronouncedly in knives (made by others) who have, as far as I can tell, either spent hours forging/welding them at hight heats, or more probably austenitized their blades for way longer than necessary.