Blisters

E

elementfe

Joined
May 3, 2008
Messages
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I've always wondered if the blisters you get in a gas forge have a specific meaning.

https://www.dropbox.com/s/r6ak1414exskdkq/2014-05-05 10.22.37.jpg

Yesterday I thought I'd be all old school and treat some O1 practice blades in the gas forge- the first one was too much in the direct blast, but the second one (actually the one on the left) hid behind a baffle while I watched for decalescence, and seems to have escaped with just a bit of scale.

Do the blisters mean that it overheated and probably has terrible grain growth, or does it perhaps come from exposure to too much oxygen?
Thanks for any suggestions!

Here's a snapshot of the entire blades: https://www.dropbox.com/s/srlrdt265dqlg4s/2014-05-05 10.22.01.jpg

Andy G.
 
Are you sure those areas are not scale and/or decarbed areas ?
 
Mete, I really don't know what they are, I'm hoping that it's shallow decarb, but just wondering whether the presence of blisters "means" something in particular.
They sand off just fine, and a few of my early blades had blisters like that and took and held a good edge.
Judging by color, that portion of the blade got just a squeak hotter than the decalescence temp.
 
I would not call them blisters unless they raise up and are hollow underneath ( as happens with damascus when there is a de-lam).

Your photo looks like normal de-carb and surface etching from things on the blade. I see it often, and after a soak in FC or vinegar it always sands away.
 
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Thanks, Gentlemen! I'm very grateful for your input.

I'll just watch how these behave, and proceed- these are just something I'm making to get familiar with forging and finishing integrals, so they'll be good candidates for some pretty severe testing.
 
When scale forums on steel, it can create all kinds of patterns. When heat treating you don't want much scale to forum, the more scale the more decarb. I heat treat in my forge and never get the stuff you are showing on those blades. Too hot, or too much time, or too much oxygen, or in direct flame?
 
Probably at least three of the four you mentioned, Don...a little more time would actually have been nice, for O1.
What bothers me about HT in general is that the edges and tip heat and cool so much faster than other parts of the blade- The only thing I can think of that would really even that out would be salt baths, but OTOH it doesn't seem to create real performance issues, it's just that we're always in search of a little improvement.

My takeaway is that a baffle, just a little "wall" between the flame inlet and the blade, helped quite a lot to keep the second blade from having scale.
Before I had a controlled heat source I did a few pieces of 440c in a stainless box in the forge, to keep the blast away while they soaked. Now, I know they would be better if they had been done in a PID oven, but they're treasured knives, and the owners think they're far and away the best knives in their kitchens....go figure- I got lucky. Some of them that I kept have pretty crappy edges, I think, didn't harden fully.
 
Ooooh...hope I don't get carbon fungus between my toes, from standing at the forge too long...
 
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