bubbles on blade after heat treatment

C

Cappe23

Joined
Dec 6, 2015
Messages
20
Hello everyone

I only started making knifes very recently but I have a little problem.
After I heat treated and tempered the blade and I've removed the oxidation layer, there are discolorations and disformations on the blade that look a bit like bubbles. I'm using 01 steel and sunflower oil.
Could anyone tell me what causes this and how to prevent it on future knifes?
Thanks in advance

Casper

EDIT: After a bit of looking around I found that it probably is scale and pitting. Can I prevend this with boric acid? And how does this work?
 
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I get it too. I'm using olive oil. To fix this problem... 2 words...

Surface grinder.
 
Usually after Ht, with an oil quenching steel, you will go back and take another .010" or so. This should take care of this. I HT at about .030"-.040" depending on the size of the blade. After Ht I take it to .020-.010" there should be nothing that that don't take care of. They do come cleaner if you give them a very thin coat of satinite, or brownells anti scale (I have t used brownells).
 
Ok thanks, but the edge is ruined as well. Should I just grind a new edge? Or next time leave more metal on the knife then I want, then heat treat it and after that finish the knife as you want and put an edge on it?
Also, sorry if my English kinda s*cks :)

Edit: And how about a mixture of boric acid and iron oxide? I'm just asking because I have these laying around at home. If I have to use something else I'll have to look for a website that sends to Belgium, since there aren't a lot of knife making shops in my area (none) :(
 
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When prepping a blade for heat treat you should leave a bit of meat on the blade as they said. Typically the bevel should be no thinner than about 0.010 thick with no actual edge put on it (it can still cut if you slide against it at that thickness though). But only leave it 0.010 thick if you want less than that as final unless you are using a vacuum oven.
 
I heat treat before I do any grinding. Full thickness.
 
I am just new in the world of knife making and I'm only fifteen so unfortunately no fancy tools like vacuum ovens ;)
Is there a way to see that the bevel is about the right thickness or should I buy one of these digital calipers.

I planned to buy a belt grinder after the exams, for making the blades but also just for wood sanding and stuff. Maybe someone can tell me if the FERM bgm1003 is suitable for the job?
I know it's far from the best but I just asked my wallet and he told me there's no money for anything more expensive. :(
 
Cappe23 said:
Maybe someone can tell me if the FERM bgm1003 is suitable for the job?
I know it's far from the best but I just asked my wallet and he told me there's no money for anything more expensive. :(
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Just a quick glance, I wouldn't waste money on that little sander, unless you want it primarily for woodwork. For knife making, your'e better off starting in investing in files.

As far as pre-HT edge thickness, I'm sure there is a proper width, but I always eyeball it (Maybe 1mm? .75mm?). leaving it thicker reduces your chances of warp during HT.

The bubble marks can be ground off, but also borax might maybe kinda help.
 
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There is nothing more expensive then buying the wrong tool. Use files until you can afford the right thing. A cheap caliper is a must have. Here you can get one for $10-$15.
 
Ok thanks, I'll stick with the files for now :)
But if I want to upgrade to a belt grinder, what is the cheapest I can look for without buying rubbish?
 
Check your austenitizing temperature- my observation is that most of the carbon steels start to get those bubbles around 1600f, which is quite a bit hotter than ideal for hardening. Also, an overly oxygen rich atmosphere in a forge is pretty hard on your steel.
 
It's hard to do when you can't control the temperature of your forge.
 
Charlie Mike said:
It's hard to do when you can't control the temperature of your forge.
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Without starting a whole new thread, could someone give me the quick and dirty on doing just that? I'm currently using a forced air forge, an I would love precise heat control.
 
Nick EBK said:
Without starting a whole new thread, could someone give me the quick and dirty on doing just that? I'm currently using a forced air forge, an I would love precise heat control.
Click to expand...

I'm using the Atlas Mini Forge so I'm in the same boat.
 
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