What exactly am I looking at here?

Drew Riley

Drew Riley

Well-Known Member
Hey guys,
I've noticed that sometimes after I heat treat a blade and grind the scale off the steel has this "irregularity" or whatever you might call it almost "etched" into the steel. It does grind out, but I'm curious as to what exactly I'm looking at, and if I'm doing something wrong to be seeing this.

5587081112_cb4e278581_z.jpg


Sorry for the crappy cell phone pic, but hopefully you can tell what it is and maybe someone can recognize what's happening here.
 
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Don't know what it is but I have had it happen when I was heat treating some 1095 your phone picked it up pretty good I never could get a good picture of it. Thanks for posting it up I'm curious
Rodney
 
Decarb and oxidation. The Decarb occurs in the heating but the oxidation can happen both there and in the quench, what are you using for quenching? Good quench oils have stabilizers mixed in to keep the oil from going off and staining, or etching the steel. Pitting is oxidation based and is controlled by maintaining a good heating atmosphere and limiting the time exposed to oxygen. Raised and rounded areas is often decarb or issues from the quench. I used to be quick to just label what I am seeing on your blades as decarb, but I have found the decarb is much less defined but quite ubiquitous. It most often is not visible on the surface without a dip in etchant and then is quite patchy, but when it is self evident it tends to be blobby or polka dot patches.
 
Carey Quinn said:
Kevin, would the decarb be caused by too much heat or are there other causes as well?

Thanks,
Carey
Click to expand...
I don't mean to put words in Kevin's mouth, but to answer your question. Heat and exposure to oxygen are what cause decarb. Higher heat will cause it to happen faster, but it will happen at hardening temp. regardless unless the blade is protected from oxygen while at heat, either by a controlled atmosphere, foil wrap or anti-scale compound.
 
Thanks for the responses everyone....

The knife in the picture was quenched with veg. oil, but I have noticed this same effect (albeit to a lesser extent I suppose) when using Parks 50.

As for my heat source, I'm using a homemade oven at 1475*F.
 
Any protective measures while heating, as mentioned anti-scale compound, foil etc...? Kiln atmospheres are very oxidizing, forges can be but have the advantage of being able to pushed toward reducing, but while this will cure oxidation, it is not necessarily a cure for decarb, but it sometimes helps.
 
Hmmm.... anti-scale compound eh? I'm gonna have to look in that. If I can save some extra grinding/scale removal time, that would really be a blessing.
 
Thanks for the answers Justin and Kieth. That's kind of what I thought but it never hurts to check up on info if you're not sure.

Carey
 
I have the same situation with my charcoal forge. The explanation that made the most sense to me was:

"Your surface blisters are either just overheating the surface, or possibly getting surface infusion of carbon (kind of like case hardening) which lowers the melting temperature at the surface where the charcoal then touches the blade and spot overheats it."
 
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