Does this look normal? What is it?

[Roger]

I'm curious about what the edge of this blade shows. It's forged 1095, heat treated, quenched in 100* canola blade first. Then tempered at 400*. I have seen this on a couple I have made and it polishes out with fine paper. I'm curious as to what might be causing it and if it will hurt anything. A file won't touch the edge but it will mark the spine.

 

[D. Crawford]

Roger, looks like your quench is giving you a differentially HT'd blade.
That is a desirable effect for alot of makers. Canola isn't the best quench
medium for 1095 so it's doing the job on your cutting edge because it's thin.
The spine being thicker isn't quenching fast enough so it remains soft.
If you sand down to a finer grit and etch in ferric chloride it will magnify
the hardening lines you see in the blade.

Also, from the look of the blade it appears you may be heating a little too hot.
Try not to go too far past critical temp and make sure to normalize after forging.

Some hand finishing here could result in a really interesting blade.

Forgive me if I misinterpreted your question and told you what you already knew.

Just my two cents worth,
David

 

[Roger]

Thanks David. I didn't have a clue before. I was heating to non-magnetic in the forge. Three times normalize prior, three times heat treat and three cycles of tempering at 400.

 

[LonePine]

I have the same situation with my charcoal forge. The explanation that made the most sense to me was:

"Your surface blisters are either just overheating the surface, or possibly getting surface infusion of carbon (kind of like case hardening) which lowers the melting temperature at the surface where the charcoal then touches the blade and spot overheats it."