why does scale form on heat treated blades?

When I surface ground the flats I just barely dusted off the surfaces. Not much heat built up because the magnetic chuck drew most of the heat out. I tried heating another blank and quenched it in water and I think I'm getting closer to the hardness I want. I won't be able to Rockwell test it until tomorrow when I go to work. Thank you goose for the advice and thanks to everyone else who gave input without people like you people like me would look like fools.
 
How tick I the blade? If it's over 3/16" you will get some differential hardening unless you really try hard not to get it, ie. Use brine.
 
I checked the blank that I quenched in water and it checks 61 to 64 and that's without a temper cycle. I finally think I'm on the right track but I am beginning to question the quality of the steel its self. Are CPM grade steels held to a higher level of quality? I have some CPM 3v bar stock that I want to start using but I want to get comfortable with my setup before I start getting into that.
 
1095 is variable from source to source. If from a reliable source, Rc66 is achievable. The heat treat is quite demanding though. I used Aldo's 1095 for a bit while the W2 was out of stock, and there is nothing wrong with it quality wise.
 
I dug this post out hoping to see an answer to my question. Since I didn't I'll post it. Has any one left the decarbonized scale on a blade? Recently I threw a batch on blade into a vibratory tumbler with ceramic media after hest treat and tempering. The blade had a unique look to it and it was smooth as a baby's butt. I'm going to leave it that way. Kind of like a stone washed finish.
 
Welcome back for your annual visit Toolin!
Your progression from a two-brick forge to a Paragon HT oven is good progress.
It would have been better to post a new thread and linked this one, but the info here is still good.

In answer to your question,
I previously explained to what the scale was - Fe3O4 - hard iron oxide. Many people like the rustic look and leave it on the upper part of the blade. On Japanese blades, it is called kurouchi, which means "Black Finish". In western blades it is sometimes called blacksmith finish or forge finish.
The scale on the lower bevels area needs to be removed to get rid of the soft decarbed steel on the surface and expose the hardened HTed steel just a few thousandths below.
Tumbling of buffing the scale can make it dark and shiny. Nothing wrong with it as long as the lower edge area is ground clean.
 
Yes, it's my bad that I don't get here very often. I wanted to post a pic of the blade in question last night but couldn't from my phone. Here is a so here is a pic. Keep in mind the blade isn't sharpened yet as I don't do that until I have the sheath finished. I posted the question more so to find out what I could call the finish on the blade. Stacy I appreciate your answer I was going to call the finish a natural finish but now I'll call it what it a forge finish. The blade shown is 1095, handle is black walnut and the pins are red oak. The total length on the knife is just under 6" and I call it a mini hunter and is my best seller.

https://imgur.com/a/OLa4wVn


I make the same blade with a finger drop/swoop hunters love them.

https://imgur.com/a/wM5Zk3O
 
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I’ve had a 52100 blade with some thick decarb you probably have to grind into it .01 at least. If your blade isn’t flat, parallel and brought to a finish beyond 120 you won’t have the most accurate reading.

Your peanut oil quench might not have been fast enough you really should use quench oil for the purpose of quenching steel. Also your hold time at temp might have been too short or too long.

I prefer air hardening steel better properties overall and you don’t need to deal with oil. You don’t even need plates if you’re not chasing max hardness values.
 
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