Patina damaged Temper of Hawkhead?

I

InSilvam

Joined
Jul 8, 2012
Messages
26
Hi,

I bought a CS Norse Hawk for me to mod. After having reshaped and sharpened the edge, I decided to add a patina by boiling the head in vinegar for about an hour. That's where the problems started.
After I took out the head, the edge looked like a hacksaw blade - all rough and so, worse than the factory edge. So I thought, well, bad luck, just gotta sharpen the head again. But as it turned out, for some reason I just couldn't get the edge as sharp as before I had applied the patina. Also, there are some tiny black dots near the edge, which for some reason just won't disappear.

Now as far as I can tell, the edge retention is still decent, and it is sharp enough to be workable (cuts through paper without ripping), but could it be that the boiling did somehow damage the temper of the hawk?

Best regards,
InSilvam
 
I think you'd have to get well above 400 F to affect temper. I doubt vinegar boils that hot.
 
Did you neutralize the head after doing this? You are putting it in a mild acid - if you do not give it a baking soda solution bath you may have areas that continue to eat away very slowly.
The process you describe will not hurt the temper given the grinding that was done before hand did not get too hot.
RMJ
 
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The grind is more liable to have hurt the temper than the boiling. You have to get it hotter then the temp that vinegar boils (roughly 215 degrees F) to hurt the temper of metal.
 
Thanks for your answers, but I doubt that the grinding damaged the temper - I sharpened the hawk using watered bench stones, so usually it shouldn't have gotten too hot. I think it could have something to do with the fact that I only rinsed the hawk with water after the boiling, instead of thoroghly washing it with soap to neutralize the vinegar (as RMJ suggested).
But by now I have it back to a workable edge, so I guess I'll just stop worrying about it. The edge doesn't need to be razor-sharp anyway, I guess.

I'm still wondering, though, why did the vinegar destroy the edge in the first place? I didn't expect vinegar to be such a strong acid ;)
 
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InSilvam said:
I'm still wondering, though, why did the vinegar destroy the edge in the first place? I didn't expect vinegar to be such a strong acid ;)
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Heated vinegar with eat your entire blade if left in long enough.

I don't want this to sound cheeky.... but how schooled are you at sharpening a hawk head? The fact that you can get it sharp has me confused. You can sharpen mild steel to shaving sharp... it just won't hold that edge for long. Is that the problem... edge retention?

One last question... After your etch, did you see a temper line about 1.5" back from the cutting edge? If not, your hawk may have never been heat treated.
 
Vinegar is just a solution of acetic acid, when you increase the temperature of the solution you speed up the reaction of the acid eating away at the metal. At boiling the reaction might have been 100x as fast as at room temperature. I think you just ate away the edge with the acid and didn't neutralize the acid when you were finished. Also, vinegar can vary in the concentration of acetic acid. Yours might have been on the strong side.
 
The hawk has a nice temper line about an inch wide, and the only problem was that I just felt I couldn't get it as sharp as before I had boiled it. Edge retention is just fine so far, I only mentioned the temper cause I was wondering whether there could be some other reason for the hawk not getting as sharp anymore (besides my own incompetence ;) )

I've been sharpening the head again now, and got it almost shaving sharp, like it was before, and it seems to hold the edge just fine. I guess I was just being a bit overconcerned and overhasty.
Although I learned for my next mod it might be smarter to put the patina on the head before finishing the sharpening ;)

Thanks for answers again, I guess the thread could be closed then?
 
Needalife said:
The grind is more liable to have hurt the temper than the boiling. You have to get it hotter then the temp that vinegar boils (roughly 215 degrees F) to hurt the temper of metal.
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This.

If you used a power tool to sharpen, you easily can burn the temper out of the edge on a hawk.
 
I have accidentaly left (uncommissioned) knives sitting in vinegar for prolonged periods to eat the scale off only to find that they were eaten significantly away. The acidity in the vinegar was pretty much completely neutralized at that point. :D

Heating speeds up the chemical reactions, of course, so it's doing the same thing as leaving it sitting for a long time.

I'd say that after the thin edge was eaten away by the acid, you're not dealing with the same bevel angles you had beforehand and that's what's throwing your sharpening off.
 
Storm Crow said:
I'd say that after the thin edge was eaten away by the acid, you're not dealing with the same bevel angles you had beforehand and that's what's throwing your sharpening off.
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Thanks - that would explain why - after putting on a new, a little bit finer bevel - the sharpening was sucessful again ;)
 
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