Gray spot on knife

R

Ryan.P

Joined
Jan 24, 2022
Messages
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Alright so this is the second time this has happen to my knives now. Right near the tang there is a light gray spot that won't come out while hand sanding. I have a feeling it is from not fully quenching but I'm not sure. Anyone know what it is and/or know how to get rid of it? Preferably without go all the back to heat treating.
 
Pics ?!?!
You don’t mention etching in your post, so this spot appears on bare metal that won’t sand or grind away.
 
We see this question a lot. 99% of te time it is decarb. Go back to the grinder, or use a hard backed sanding block and remove a few thousandths more metal. I bet it disappears.
 
Stacy E. Apelt - Bladesmith said:
We see this question a lot. 99% of te time it is decarb. Go back to the grinder, or use a hard backed sanding block and remove a few thousandths more metal. I bet it disappears.
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I just posted pics. I have the feeling it's the depth of my quench tank or over heating the tang at the grinder. What do you think?
 
That looks like a "transition line" where the steel has a change in crystal structure and mix and could be entirely attributable to not getting it into the oil.
 
fitzo said:
That looks like a "transition line" where the steel has a change in crystal structure and mix and could be entirely attributable to not getting it into the oil.
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I'm assuming another quench would be the only fix the "transition line"? Also It's held up to a few test but if this is the case would it be safe to assume poor structural integrity at the transition?
 
Correct, it would need another HT cycle and a full submersion in the quench medium. Fortunately, looks like you have most all the cutting edge hard.

No, not poor structural integrity. It's a "quench line" or very bad version of a "hamon" is all. Steel will be softer behind the line than in front. You could verify that with a file perhaps. Not a biggie, just not so desirable right there. I've done it, too. You're lucky it didn't warp.

Finish the knife and keep it around for humility and the lesson.
 
fitzo said:
Correct, it would need another HT cycle and a full submersion in the quench medium. Fortunately, looks like you have most all the cutting edge hard.

No, not poor structural integrity. It's a "quench line" or very bad version of a "hamon" is all. Steel will be softer behind the line than in front. You could verify that with a file perhaps. Not a biggie, just not so desirable right there. I've done it, too. You're lucky it didn't warp.

Finish the knife and keep it around for humility and the lesson.
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Yeah the edge held up for sure.

If I remember right that one did warp a little right there.

I've got a pretty respectable "knife graveyard" going in the shop. This will be a lesson I don't want to learn again. I got a deeper tank to handle these longer knives now.

Thank you all for the help I really appreciate it.
 
Ryan.P said:
It is not deep enough and that is my feeling because the other time it happened the tank was not deep enough as well..
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I have a knife I kept for myself, it has the same issue, about a half inch is a different color after etching because my tank isn't deep enough.
 
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