Hitachi white #2, carbon diffusion

Willie,
That might be it. Next time I get to work on them I'll grind them a bit more and see if that helps. Maybe I didn't grind them enough after the HT. I worked from 80grit to 400 on the belt sander , then hand sanded to 2,000. I didn't expect it would be decarb because I assumed I ground off enough material. But I did rush a little the day that I ground them post HT. And hand sanding doesn't remove

Definelty something I didn't even think of. Better to give that a try before completely re HTing the blades.
 
It’s been a long while since I last worked on the two knives in this post. Figured I would add onto this post instead of making a new thread as an update.

I’ve been home from school for winter break and was able to grind the blades more. It did turn out to be decarb that was causing me problems. I only got around to hand sanding the sheep’s foot blade, I brought it up to 800grit then etched in hot vinegar.

I etched the blade 4 times for 5min each time, rubbing the blade down with some 1,200grit paper between etchings.

Pictures: https://imgur.com/a/v7wpf

The line closes to the edge is the lamination line, and the line just above that is the auto-hamon line. The hamon line has very crisp detail, it’s hard to really capture all the detail on my phone’s camera. It has almost a “flakey” look to it, like chipping paint. It’ll be exciting to take the finish higher and show more fine detail.

I’ve come to the conclusion that the auto-hamon line is not from carbon difussion, but the mild steel cladding hardening slightly. I’ve worked on several other blades with full flat grinds (each with different steels, 1075, 15n20, homogenous white#2) similar to these blades and have been unintentionally getting auto-hamons. I’d assume that the geometry of the blade helps this happen. Hopefully when I have more time to work on my blades again I can learn more about clayless hamons. I just received my Evenheat Kiln yesterday, so now I should be able to figure out exactly the time and temps to get hamons like this. Should be a bit more “scientific” to keep track of variables over my stop watch and gas forge technique.

Thanks to everyone who helped out,
Kevin
 
It's definitely carbon diffusion. It happens all the time in sanmai blades. 30 minutes at normalizing heat will cause some carbon to move. Also, when this material was forge-welded before you got it, carbon was moving into the cladding. It's just the nature of the beast.
 
Yep, not an auto-hamon, just the line of carbon diffusion from the weld. You could consider it a Heat Affected Zone.
 
Ah ok, thank you guys. So I guess I was on the right track initially with the diffusion.

I’m glad these blades turned out well from the HT, over the holidays I got more hitachi white and some blue #2. Hopefully when summer comes around I’ll get some time to try out these steels a bit more.

Thanks again for the help,
Kevin
 
Again another update for this thread.

I have been able to work on polishing my knives again and I think I have all the full story now. The thin “flakey” line I assumed was the detail from the carbon diffusion, is actually the line from the lamination. And the heavier line might actually be some kind of “hamon” like line. Here are some pictures that should help show this: https://imgur.com/a/osxBL . As you can see the fuzzier line actually starts in the mild steel cladding. Then it slopes down into the white steel core. Then towards the tip of the blade, curves back up into the mild steel cladding.

It is also interesting to see that the part of the white steel core above the “hamon” does not have a grainy appearance like the rest of the core steel when etched, in comparison to the cladding. This small detail leads me to believe that this is actually an auto hamon, not a line from carbon diffusion.



So far from working with white steel on these knives and others I have found that it has a lot going on in its structure. Maybe this is from the way it is produced at the Hitachi factory? Even when etched before hardening it appears to have a “grainy” structure. then after hardening, etching, and polishing the “grainy” structure becomes more pronounced. These blades are really benefiting from a differential polishing due to this, giving them beautiful contrast.

I know I’m almost beating a dead horse with this, and this thread has been going a while. But I keep learning more and more about the structure of these blades as I go. I thought it would be good to share this here so you all can see what’s going on too.

Thank you all again,
Kevin
 
You must log in or register to reply here.
Back
Top