Edge temper burned

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Dec 28, 2003
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On a HI standard Katana sword I bought last summer (Bura), I noticed a blue mark on the edge of the blade and asked about it online at the time but got no responses. Somehow I failed to notice until today that this mark also is on the other side of the blade in the same place on the edge, although a bit broader and longer, just below the sweet spot about 1/3rd the way up the blade.

Now with a bit more experience and reading behind me, I realize that this mark was made by someone polishing out the edge of the blade, and holding the blade too long in one place and overheating the metal. The mark is a brownish-blue in color, and my question is, how damaging is this and can it be fixed? The temper has obviously been removed from this small section of the metal. Does that make it brittle, or too soft?

In Blade magazine a guy mentioned reheating this section and then requenching. Do you think that would work to retemper the damaged blade section?

Any tips from the knifemakers or mettalurgists out there would be welcome.

Thanks!

Norm
 
Your observation seems correct.
Was it sold as a blem because of this?

The colored area would be softer.

Many people say temper when they mean harden,
it can get confusing.

Tempering is, in part, a softening process---
that accomplishes other ends.

It's not possible to harden just a spot on the edge of the blade.
Hardening requires heating to a very high (& specific) temperature range,
then quenching-----cooling the steel rapidly.
To try to heat just a spot on the edge,
without raising the temperature of the edge beside the spot
is just not possible;
at least in any practical affordable manner.

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Norm, that would make it softer. If you've used it and it didn't roll or bend, it's ok. How wide is the discolored area?
If it's between the "sweet spot" and the cho, it's probably not real hard there anyway.

Steve
 
Interesting. I have always wondered about the effect of polishing, because I have had edge rolling on polished ones only and had villagers with just as thin of an edge that didn't roll. Maybe just luck of the draw but I always wondered if the polishing was heating it up to much and that was accounting for it.
 
donutsrule said:
If Norm's katana has a cho, then there are larger issues with the blade...

Obviously I get an "F" in reading comprehension. :eek: I didn't see the katana part. Oops. My bad.

Steve
 
Careful, Steve, that sounds a lot like an explanation to me ("Never explain, never complain.")
 
If its brown/blue it has probably still something like 52-55HRC. I had some arrowheads which I tempered for this colour schema after heat treating and they were still too hard.
 
Traditionally this would be considered a fatal flaw in a katana or other Japanese sword.

It can be fixed though, but it would be cheaper to buy a new one.

If you want to fix it you'll need to re-differentially harden it.
 
hollowdweller said:
Interesting. I have always wondered about the effect of polishing, because I have had edge rolling on polished ones only and had villagers with just as thin of an edge that didn't roll. Maybe just luck of the draw but I always wondered if the polishing was heating it up to much and that was accounting for it.

I should have figured it out, as I saw the same discoloration once on an old straight razor I was trying to salvage. I used a hard polishing wheel on my Dremel and was happily removing rust when I held the wheel too long in one spot. The metal was so thin anyway that it immediately burned, and that looked just like this damage. I don't think normal polishing or edge sharpening has any negative effects, but your experience with the villagers is telling, and maybe you are right? I know a buffer can get the blade damn hot if not careful.

Dean, no it wasn't sold as a blem, it was one of several lots of khuks I ordered from HI directly in the middle of the year during the height of my terrible HIKV addiction. My neighbors must have thought I was an HI distributor or something, and I about wore Uncle Bill out there for awhile!

The reality though is that because I was buying several pieces at a time, that Uncle Bill generously gave me what pretty much amounted to blem pricing on it. It is my second HI Katana, the first being an Everest kothimoda with carved horn handle that balances like a dream because if has a full length tang which weights it towards the back, and a steeply curved blade. It just naturally sits back in your hand and wants to slice. I bought that one from another forumite.

This one is the standard katana with the 8 sided wood handle, uncarved, with a brass buttcap. The blade is only slightly curved and even though it is 5 ounces lighter than the Everest Kothimoda katana, it actually feels heavier. The sheath is perfectly done. The blade came sharp, which was a surprise.

Ferguson, the damaged area is about 40% up the length of the blade from the guard, and is 1" long on the left side of the blade, and a bit over 2" long on the right side. Most of the cutting action would probably start just above this area, and I suppose I could roll out the metal if it did turn. I would just be afraid of it breaking out.

Frankly, at this point, my concern is mainly cosmetic; I'm sure I won't have a problem with it, but I can't get it to polish out, and it ruins the looks of an otherwise nice piece of work.

BUT, I suppose I could blue the whole blade though??? That would hide 99% of it...

Thanks for all your feedback and good info.

Regards,

Norm
 
Cabbit said:
Traditionally this would be considered a fatal flaw in a katana or other Japanese sword.

It can be fixed though, but it would be cheaper to buy a new one.

If you want to fix it you'll need to re-differentially harden it.


Cabbit, do you think it could be done? Could I heat just the entire edge and then quench just that? Would that remove the discoloration? I know I would have to be very careful not to quench too high up on the back of the blade.

Thanks,

Norm
 
Actually what you need to do is add a thick clay slurry all over the blade (satanite works best) then when it dries, scrape off the clay along the entire edge on both sides.

Heat up and quench in water.

It sounds easy, but it's very tricky. I'd have someone who's done it before do it, or get advice from people who do it all the time.

This will add curve to the blade.

If you botch it though, the blade will shatter.
 
Cabbits quote.


" (satanite works best) then when it dies"

Cabbit your not a vampire slayer by any chance are you?

Spiral
 
Take a file, try hardness of steel in "damaged" area. The discoloration can be only on the surface.
What are you intending to cut with the sword?
Post a photo.

It is known that many japanese swordmakers have used engraving for hidding of blade flaws, so I wouldnt care much about them.
 
Again I wouldnt try to heat treat the sword again, only very few people can do it. Not even god knofemakers can do, sword are animal of different stripe.
The blade on edge is probably too thin for another heating, even if you use clay or another stuff.
 
hawkwind said:
Take a file, try hardness of steel in "damaged" area. The discoloration can be only on the surface.
What are you intending to cut with the sword?
Post a photo.

It is known that many japanese swordmakers have used engraving for hidding of blade flaws, so I wouldnt care much about them.

Certain types of flaws are cosmetic.

The type of flaw he mentioned, if it isn't a simple discoloration is very much a fatal flaw.
 
Svashtar said:
Frankly, at this point, my concern is mainly cosmetic; I'm sure I won't have a problem with it, but I can't get it to polish out, and it ruins the looks of an otherwise nice piece of work.

Regards,

Norm
Norm it will polish out if you use the proper materials and method of polishing. I bet if you rubbed it with 0000 steel wool or 1,000 - 1,500 grit paper for a while you would start seeing the steel gray color. Somebody had too hold the blade in one place very hard and for quite a while for it too discolor!:( :grumpy:
 
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