What are these circles?

Scott Hartman

Scott Hartman

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Oct 28, 2005
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I'm still a rookie at knife making. This blade is forged 1084, clay coated and quenched in mineral oil. Blade was normalized,annealed & tempered. I use a gas forge. After etching the blade, these circles popped out. I hand sanded the blade again, cleaned thoroughly, re-etched...still there. First time I've accomplished this...what did I do wrong?
 

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Probably decarburisation, the lower cabon steel etches differently from the higher carbon steel or could be unharden areas, try a scratch test.
 
At first guess, crop circles. I've seen something like that once before and had the same thing happen after sanding some more and etching again. I couldn't figure it out. I think I may have even hit it again with the grinder and they still were there.
 
I'm bettin if you HT again with a longer soak your circles will disappear.
Matt
 
I'm guessing decarb, but I am just guessing, how much did you regrind after your heat treat? if you only took off your scale you likely have a thousandth or 3 to go before you get to the bottom of your decarb's deepest regions, ut as I said I'm guessing and certainly not an expert. I'm waiting to see what Kevin and Mete say.

-Page
 
It can be caused by several suspects. First overheating the blade. This is normally a more cottage cheese effect though. You have almost perfect circles. Second bubbles insulating the blade on quench. Did you agitate the blade in the quench medium? This helps to eliminate the bubbles on the blade. Finally it can happen in the etch also. Bubbles can form on the blade from oils or just not getting a good contact with the etch solution. I use an aquarium pump with a diffuser in the bottom of my etch tank. The rising bubbles remove any bubbles or residue from the blade when etching. Try a light sanding with 1500 grit and put it back into the etch. If that does not work then I am afraid it is normalize and re HT the blade.
 
Chuck, I have gotten bubbles in the etch but they would be random each time you etched. I think its just a phenominone............
 
Karl B. Andersen said:
Nope - poltergeist circles.
I'm sure of it.
(You knew this was coming, right Scott?)
Click to expand...

Oh yea, almost I almost posted this thread as Crop Circles. I think I'll re-normalize and heat treat. I may have over heated the tip as Matt suggested. As sunshadow pointed out, I thought it was in the decarb below the scale, and did hit it back on the grinder, re-sanded & etched...no change.
I'll set it to the side, finish the knives I've got, and re-HT with the next ones. If the circles disappear, I'll update this thread. There's a lot of great guys on this forum, always willing to help out and share their knowledge.
 
I believe it shows an area that did not harden due to bubbles in the quenching liquid. What did you use? What else would show up as round when etched. It doesn't look like alloy banding. Hardened steel etches faster than unhardened steel. If the circles are soft; You should be able to see the difference under a good magnifying glass.
Moving a blade from side to side when you quench makes a lot of sense in achieving the maximum results.

Fred
 
I have had this same problem a couple of times. It has to do with the bubbles formed in the oil while quenching. I never etched the blades but you could still see the circles.
 
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