The trials and tribulations of heat treating 80CrV2

[Laredian]

Recently made two small edc knives from 80CrV2. All went well and I was a happy cat until I started heat treating them.
I have tried multiple protocols for 80CrV2, but I personally have had quite good and consistent results using Larrins recommended protocol which you can find in his book and also on knifesteel nerds. So far so boring, 80CrV2 is a quite forgiving steel in my experience, but these two knives just wouldn't harden, like at all.

Did some thermal cycling at 850C° for 15min and then at 815C° and then tried hardening again, but to no avail. I used some anti decarb to protect the blade during the process and ground the blade further before checking hardness.

I am not sure what exactly went wrong. I've heat treated a bunch of 80CrV2 with Larrins recommended protocol with good results.

My only guess is that I've either got a bad batch of steel or this bar came in a state which needed higher temps in thermal cycling? I don't know, I've scrapped the blades and started over with another bar of 80CrV2 which hardened just fine (I made a coupon and checked that one beforehand).

This is me just basically venting a bit and saying don't change your supplier. Because the bar that gave me trouble came from another suppler than I usually order my 80CrV2 from. Also that bar, which gave me trouble, strangely had a very thin hardened layer on the outer edges of the steel which my bandsaw couldn't really bite into, I had to make a notch with my anglegrinder and then I could saw into it....I've never seen that before.

 

[Stacy E. Apelt - Bladesmith]

First - make sure that you fully ground ALL the decarb off the blade before checking the hardness. After that forging and other thermal cycles there could be a good layer of decarb.
How did you test the hardness?

 

[Laredian]

Yes, I am very positive that I ground off all the decarb. There was just shy over 1mm of material thickness behind the edge when I hardened it, after hardening I did an ol' super duper accurate file test, but the steel was so soft that I thought I must have a stronger decarb layer than usual so I worked the grinds a bit and brought the primary grind down to about 0,4mm thickness at the edge.

Didn't even bother testing the exact hardness at that point because the steel was still completely soft and the edge and the tip deformed quite a bit after some light testing. And I'm not talking about chipping but dents. The material didn't break off, but was rather pushed in and smushed aside after lightly whacking it into some antler offcuts.
Usually I can whack hardened and tempered 80CrV2 knives into mild steel with no damage using Larrins protocol.

Edit: this is just anecdotes and not scientific data, but I've never had a problem with 80CrV2 before regarding massive decarb layers and the steel appearing soft.
I don't know an equivalent product in the US, but I use an anti decarb spray which dries like a layer of paint. Can't describe it better, but it has worked quite well thus far and was specifically made for heat treatment applications.