Nasty spot on my blade

B

Brad Lilly

Moderator and Awards Boss
I'm sanding up a blade I forged out of 1084 and this funny spot shows up. I'm pretty sure I know what it is but I thought I should see if anyone else thinks the same.
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Sorry for dropping the thread. I'm thinking I have a case of knife chicken pox. I ground the sucker out and etched it again and the bloody thing is back.
 
What was your HT process and quench medium? I had an odd spot appear in a 1084 blade not too long ago but it was larger than that, I finally deduced that it was an un-hardened spot caused by the slotted fire brick I used as a blade fixture in my HT oven casting a heat shadow on the blade. I won't suggest that yours is the same issue, and could be wrong about what caused mine in the first place, but without some additional info the best input you are likely to get will be guesses.
 
I’ve never seen anything exactly like that, but they look like (and by your description) some type of inclusions. Since the individual lines seem to be oriented and elongated in the direction of the rolling, they look like the deformable type. Possibly a cluster of tiny stringers.
 
I don't think my heat treat caused this because the tang is used to hold the blade edge up and I quenched the whole blade in Parks 50. I never touched the blade with anything other than quench oil.
 
Brad Lilly said:
This is exactly what I'm worried about.
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… as it should.

However, the size and location of inclusions does play a role. In this particular example, (if that’s in fact what it is), it’s not what I would consider large and it’s location is not near the edge. So, that one or “cluster” is probably more of a cosmetic worry than a structural one. On the other hand though, most of them go un-noticed and/or are internal. It’s safer to assume that more are present, could exist in the worst possible locations and could lead to structural problems, than not. Stresses in heat treating can aggravate, make these “spots“ worse and lead to more problems and surprises.

My personal opinion is that the Parks #50 is a faster quench than necessary for this steel and blade geometry, and may be doing more damage than good. However, if the blade was forged to the edge it would help break up, “string out”, refine and minimize these potential problems, worries and concerns, as would using a bit slower quench oil. If the blade was properly forged to the edge, it would theoretically improve it’s ability to handle the rapid quenching along the edge where it's the most important.

I’m not singling you out or picking on you, but using this an example that we might be able to learn from. This type of thing is not uncommon, but rather typical and happens quite frequently.

Short term, in shop type performance testing can not always guarantee how the blade will perform in the long run either, they tend to fatigue faster when these types of inclusions are present and/or aggravated by unnecessary and/or extreme thermal stresses.

There are numerous variables that can have an effect, so I’m in no way suggesting that your blades in general are inferior or any worse than the majority of what’s out there. I'm also not absolutely sure what the "spot" is, just using it as a point for conversation.
 
I’m not singling you out or picking on you
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Yes you are it's obvious :) (I'm kidding of course).

I have used the parks 50 on a few knives so far and I have been pleased with the results. 1084 is a nice forgiving steel. I do try to forge as close to size as I can get away with, sometimes I think that causes more grief then a little more grinding

So far I have chopped a 2x4 twice (that is full size white spruce) with the knife and the edge held fine. It passed the brass rod edge test so I'm not too worried about it but it is a little too ugly to sell. I'm thinking it will become my EDC.
 
Sounds like a good plan... do some long term field testing on it. Good to have a few of those to test for long term performance, feel, balance etc.
 
Brad Lilly said:
I do try to forge as close to size as I can get away with, sometimes I think that causes more grief then a little more grinding
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There was an old bladesmith “myth” that has been widely dismissed, “never forge a blade edgewise”,… seems like upsetting (mushrooming) a stringer could have the opposite effect as forging reduction along the edge, aggravate and open it up.

I think a bit of stock reduction (grinding back etc.) at the edge makes sense... on forged blades, always a few stresses etc., at the edge, even with straight down reduction.
 
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so how do you keep finger printer off of your knives?? or at least not inpack the steel and causes spots?? anyone??
-Young Pup
 
... don't get sweat in your quenching oil.

If you do, you'll here a crackling sound when you quench your blade and get funny little soft spots.

The salt in sweat can also contaminate the oil and speed it up,... this can lead to blades warping and cracking.
 
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