Hello,
I am trying to make hamon lines for the fist time, using 1075 from NJSB. My normal process is to polish my blades to 220 grit before heat treat and use PBC anti-scale. After quench the anti-scale comes off easily and the blades are for the most part ready to polish to 320 grit and continue.
For the hamon I used Imperial furnace cement (rated to 2000 F) from my local hardware store. I applied the cement, air dried it 1 hour, then baked it using a 3 step ramp to go up to 400 F to make sure it was dry. Next I applied anti-scale by preheating to 615 F, then heat treated at 1500 F and quenched as usual. Everything seemed to go well until I removed the furnace cement. Under the cement, and especially around the edges, there were a lot of pits in the steel, which is requiring significantly more grinding/polishing than I have needed to do since I started using the anti-scale. I should note also that away from the furnace cement where the blade was protected by the anti-scale the steel is fine, as usual.
Are these pits to be expected? Is there a difference in the amount of pitting between different types of furnace cement and/or clay used to create hamon lines? Is there some process steps or detail that reduces/minimizes pitting when creating hamon lines with furnace cement?
Thanks,
Dave
new guy here so take this with a grain of salt and a more experience smith can chime in and correct me if I say something wrong. I have been playing with 1095 a bit and get hamons but I never use any clay. I will grind the blade back maybe 3/8 of an inch from edge and leave around a dime thick or tad thinner to avoid warping. Then I ( I know this kinda redneck but it works) preheat with plumbers torch so the steel is between 500-800 deg'ish. I can see a slight heat wave in it when I put into forge. Right from quench in P50 while still to warm to grab it goes in between 2 1/2 thick aluminum plates and is clamped. After temper it can be ground flat past the initial grind and pretty often reveals a very nice subtle human line with zero pitting. I know it is a different process but it is worth giving a shot on some material to see for yourself. Good luck man 🙂
Minimum Effort = Minimum Results every time
It's evident to me that that this combination of steps in the process is something the steel doesn't like. I have not used that process. It's often a matter of changing the process and eliminating the thing that is causing the problem, in the case, pitting.
The point in using the furnace cement in conjunction with the PBC is, obviously, to save going back in the grit sizes to 180 or 220, right? However with your process you still have to go back to larger grit and get out the pits. What the difference between going backwards for pits or going back for scratches? Not much. BTW, the scratches will likely be more consistent than pitting. I would prefer the scratches.
So I would change my process.
It's evident that a form of surface oxidation or spot burning (my words) is taking place. I don't know but it might be a reaction between the furnace cement and the PBC. Is it happening where they meet? Localized?
Having done many hamons I can feel your pain.
It seems the edges of things somehow isolate and locate the heat literally helping to burn the steel.
The simple solution is to leave a little extra meat on the blade and grind it off afterwards.
Don't spend so much time trying to make your blades "pretty" before hardening. When I do hamons I harden directly off the grinder at 220 with NO hand sanding what so ever. I'm going to regrind afterwards anyway.
Karl B. Andersen
Journeyman Smith
I thought I should also mention that I use a forge for my hardening. I only ever got the pitting when I used my oven. The atmosphere is entirely different with the fuel burning up the oxygen. I'm positive this has something to do with it.
Karl B. Andersen
Journeyman Smith
had to shrink pics some for forum, this is the result post being told to remove the saber grind and revealing the auto hamon created from the shaping preheat......hope it helps some.
Minimum Effort = Minimum Results every time
there is pletty grind wise wrong with this blade honestly, but for the purpose of poster's making a hamon. It does a nice job of a not busy and clear line.........any advice you fella's have to send my way are also appreciated 🙂
Minimum Effort = Minimum Results every time
David, personally when heat treating for a hamon, I only go to 120 before heat treat and that is belt finish. I just use satanite. I will leave the edge a bit thick, say fifty thousandths. I know I will be grinding after heat treat anyhow. The furnace cement should work fine, but the pits may be because of the furnace cement as some have things like lye or other corrosive materials in them. It may be a reaction between the cement and the pbc coating. The 1075 should produce a nice hamon, but I would suggest doing without the pbc coating and plan on some grinding afterwards.
Brion
Brion Tomberlin
Anvil Top Custom Knives
ABS Mastersmith
Gentlemen,
Thank you for your replies, there is some good information there. Girnie, that is an interesting process you described. I have heard of a few different processes to get hamon lines but I was going for the "classic" scalloped edge which is why I used furnace cement.
Lin - you are correct, I did that process to try to minimize polishing after HT but obviously it didn't work. It was my first time so I have no problem changing for next time. The pitting also occurred elsewhere under the cement, so it was not just where the cement and PBC were in contact, although it seemed worse there. So I can't rule out an interaction between the furnace cement and the PBC anti-scale but there are also other factors at play.
Karl, Brion - My take away from your comments is that this is expected. I understand the difference in the atmosphere between a forge and a furnace. The pitting reminds me of what I used to get heat treating in a furnace before using anti-scale, so I am assuming it is a some sort of localized oxidation. I guess I thought the furnace cement would protect the steel from that similar to what the anti-scale does, but obviously I thought wrong. It may indeed be due to localized components in the cement interacting with the oxygen and steel to cause severe oxidation, since it is very non-uniform.
For next time It looks like I have 3 choices: spend less time on the blade before heat treat and plan to spend more time afterward grinding and polishing, heat treat in my forge rather than my furnace, or find a cement or clay coating that also protects against oxidation. If anybody knows of one, I'm open to suggestions!
On the brighter side, I'm mostly done with the grinding/polishing now and I can see the hamon lines clearly, so overall it worked!
Thanks again,
Dave
