CPM 3V surface decarburization?

To start out with-



Steel is njsteelbaron .217 thick CPM 3V. 2000 degree austenitizing, 30 minute hold, plate quench and what will be a 950 degree triple temper. These photos taken after the first temper cycle and a light grind done at 50g to show detail.

There is a layer, line, or differential in the steel just barely under the layer of surface decarb. I did no grinding to the flats prior to heat treatment as I had chosen to not use foil, wanting to leave as much sacrificial thickness as possible. My choice of not using foil was to speed up the plate quench as I've found this steel super-tricky in the past. What do you all think this line might represent? Thank you in advance!

I suspect with 2000 degrees for 30 minutes - with no foil, you have way more than surface decarb. - at least to the depth the line is at. Also wondering where you got 975 for tempering.

FWIW, I've had excellent and consistent results using foil and plate quench. (And we double wrap - two envelopes)

CPM is powder technology. The powder is put into a canister (not sure what kind of steel the can is), heated and rolled. What you see there is the remainder of the can rolled out very thin. This is one of the reasons that CPM steels are so grossly over sized. It doesn't really hurt anything, consider it a feature if you like. Most of the time, everyone grinds this stuff off as they clean it up to clean metal.

Thanks for the info, Tracy. That explains it. This particular piece of metal had a couple of things going on that I hadn't encountered before but it's all been resolved.

kinda wondering where the 950F for temper came from. sounds a little low. http://www.crucible.com/PDFs/DataSheets2010/ds3Vv1 2010.pdf
scott

At that temp and those times with no foil, the decarb could be quite thick. Maybe it's just me but vanadium bearing steels seems to decarb fast, if given the opportunity.

You lose hardness pretty quickly once you bust 1000F. with the temper, according to Crucible's specs, and a lot of folks like the way it performs at 60-61, so the slightly lower tempering temperature seems to be common.