Problem heat treating 80Crv2

If they are just sitting in the oven, the decarb will not be significantly more severe. Yes, there will be more, but it won't be because the door was opened and closed. There is plenty of O2 in the kiln already.

As Knight Owl Forge suggested, a thin coat of Satanite or other refractory liek ATP-641 will greatly reduce decarb. I don't worry about it, as the decarb grinds away quickly. IT doesn't need to be more than a thin wash coat to help.
 
I mostly use atp-641, but as Stacy says decarb in the 1500f range is a slow and shallow phenomenon, so no biggie either way.
I can never remember the exact triple quench deal, but why not just normalize / grain refine by repeated austenitizations sans quench. Not sure there is any benefit to repeated martensitic transformations outside of something like a double hamon or something.
 
he conversion to martensite …. at least on the last heat …. is because martensite is the best starting platform for the austenite in final hardening.
 
I repeated the heat treat following your instructions. Using my crude heat treat file set, the estimate is between 55 and 60. One of my grinds was going downhill, so decided to break it in the vice to see what it looked like.

How does this grain structure look?
689dw3T.jpg
 
It is really hard to tell grain structure with broken samples like the one shown. There is usually going to be some tearing/stretching of the steel that affects how the grain structure really looks. Tempering makes this tearing/stretching worse, and is best to do a clean break the best you can immediately after quenching, prior to tempering. If I understand correctly, this sample was already tempered and you were already grinding it.

With that said, it looks good, better toward the edge itself than the spine...but again, it could be what I described above. Next time if you want an idea of your grain structure, do it after quenching before tempering. When I've done it in the past, I'll take a dremel cut off wheel and score one side of the blade where I want it snapped. Just a shallow cut, and really not necessary. The grain structure should look like what I describe as "gray velvet". Just a smooth surface without any grain structure to it. The real way to check grain size requires a bit of prep work...polishing, etching, and microscopes.
 
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