Heat treat problem

smitty0331

smitty0331

Joined
Dec 5, 2006
Messages
892
I just finished a blade O1, 3/32'' thick and ht'd it, the problem is, when I checked it with a file, it wasn't hard. I took it up to 1475-1500 deg. held for about 10 min, then quenched in 100 degree oil. The oil may have cooled a little, maybe 90-95 deg. Any idea where I went wrong?
 
Was the blade forged? If so you may have some decarb on the edge. Also is 3/32 the spine thickness or edge? How are you judging temp? The oil could have been a little hotter. But then again what type oil are you using? I take my slow quench oil to 150-160F but his should not have made that big of a difference. It is hard to say exactly what went wrong but this is what popped into my head (lots of empty space).
 
Some possibilities...

Are you sure it was O-1.?

What was your heat source..? Any possibility of
Decarb..?

How much time elapsed between withdrawing the blade from
the heat, and getting it into the oil.?

What kind of oil..?

EDIT...Looks like Mr. Richards typed faster...!
 
Isn't decarb the black stuff on the blade after ht? Yes, I did have the black stuff, if decarb is what it's called. My heat source is a 2 burner propane forge, and I have a good digital controller wired to a tc wire. My quenching oil is used trans. fluid heated to 100 deg. aprox.
 
Decarb is where the carbon is burned out of the surface of the steel
in an oxygen rich atmosphere. It can be deeper than the forge
scale. If the problem is decarburization, you can tell by grinding
down a bit to see if the steel is harder beneath the surface.
Most decarb occurs outside the forge...in open air.

I'm not sure what qualities to expect from tranny fluid...only that
the fumes can present a serious health hazard. If you don't have
access to a good commercial quenchant, like Parks AAA, or Brownell's
Tough Quench, try Boiled Linseed Oil. It was a recommended quenching
oil for a long time, and works well for O-1 and 5160.
 
I've had this w/ o-1 before. Take a couple passes on your grinder on the edge and check it again w/ the file. Some o-1 seems to decarb [lose carbon & remain soft] worse than other. It may be hard a couple thousandths in.


:eek: ok,what Russ said!! :D
 
Right now, I have the blade in my toaster over for the first of 2 400 deg. cycles for an hour and a half. Should I continue with ht. or start over? If I start over, can I just put a piece or two of charcoal in my forge to alleviate the problem? I'm not exactly sure what course of action to take, I'd sure hate to lose that blade.
 
The first thing to do, I think, is to determine if the blade's surface
is decarburized. If it is, requenching won't be productive. Remove some
surface material and see if it's harder inside....hopefully it isn't.
If it isn't, that just means that the blade was probably underheated,
and requenching from the proper temp could get you a hard blade.

If it'd harder beneath the surface, I'd say it's probably scrap, because
being only 3/32"thk, if you remove the decarb, there wont be much left.

If decarb isn't the problem, try rehardening it, but don't depend only on the
controller. Watch the colors change...first dark red then lighter...then
when it's near orange, it will get darker. That's the transformation taking place,
(decalescence).....then it will start getting even lighter than before. When
the whole blade has passed decalescence, see what the controller says, then
quench...quickly. This will get you a hard blade, and give you a rough idea
if the controller's probe is in a hot/cold spot.
I'd forget the tranny fluid.

If it gets properly hard, then temper at 450 for two hours, twice.

...Hope some of this helps...
 
Here are a few more questions that need to be answered if possible.

What was the source of the O-1?
Have you tried going deeper with the file than just a surface pass?
How long between removing from the forge to quench?
How hot was the steel when you removed it from the oil?

If you are using a gas forge think about using a muffle, this is a pipe that is inserted into the forge to bring the whole thing up to temp. The nice thing about a muffle is you can put some charcoal into it and it will produce an inert atmosphere. If you put the charcoal into a gas forge it will just burn up. Here is one link I found with a quick search http://www.bladeforums.com/forums/showthread.php?t=477624&highlight=muffle
 
Smitty,
You're sure welcome...also, what Mr. Richards said about a muffle is a
great idea.
 
Thanks Mr.Richards. I sure do appreciate the help. I think I might have a problem though. After my unsuccessfull hardening, I still ran it through 2 ht. cycles. Since I can no longer check to see if it is hard below the surface what can I do now?
 
When you say "2 HT cycles", what do you mean..?
Why do you say that you can no longer check below
the surface..?
 
Your Very welcome. HTing can be a pain. I am still wondering if you forged this material though?? If you did it has probably decarburized more than you would desire.

Please call Me Chuck... when someone says Mr. I look around for my father.
 
I didn't forge this blade, it's stock removal. I hit the edge 3 times with light preasure and it started getting harder, so I think I'm just going to take it back to about 110 grit bels and re-finish it since it seems to be pretty shallow. By 2 cycles I meant that I heated it at 400 deg. for 1 1/2 hrs., let it cool, and heated it again at 400 deg. Does anyone disagree with my plan?
 
Just curious here. Did you check to see if your blade ever got nonmagnetic? Just wondering if your controler could be off.
 
If your heat control is working properly, your problem is decarb. Before you Ht again, buy some PBC powder, and use it. It will stop the decarb in it's tracks. 1500°, for 15, to 20 minutes in soak. then temper at 425°, to 450°. Two, two hour tempers. It is best to do a twenty minute soak at 1250°, then bring it up to 1500° for the 20 minute soak before quench.
 
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