Heat Treat S7 - Pictures of Pre-temper steel or of scale?

[halzucati]

I'm looking for some pictures for comparison of a post-heat treated piece of S7 Steel.
Using Crucible specs for heat treat I want to see what the steel comes out of the kiln looking like..
Something heat treated + - of the following:
1350 soak for 2 hours
1725 soak for 25-45 min
air cool

What I want to see is some kind of typical result as I have not been able to find any pictures of post-heat treat steel.
I'm not using foil or coating of any kind...
Heat treat naked steel
Air cool naked steel
Temper naked steel.
Anyone help me out with some pictures of what this looks like?
What I'm experiencing is a layer of black material that is uniform over the entire surface of the metal I've heat-treated. As the metal cools this material literally pops off and crumbles when touched leaving a dark smooth finish on the S7 steel.
I think what I'm dealing with is either oxidization or decarburization or just normal S7 heat treat scale?
The material I'm using is 12" x 2" x .25" thick.
The finished product is both strong, resilient and durable and has held up to all the tests I've been able to think up and perform on it. I'd just like to know if this is common or something unique to what I'm doing.
RC is between 55-60 using a numbered file set and the scratch test. Its closer to 60 than 55 as the file does not want to bite much, but it does a little. The 65 bites right in.
Thanks!
- Hal Zucati

 

[Daniel Fairly Knives]

It sounds like you are decarbing your steel, I'm surprised there was any steel left!

Use foil next time and the steel will come out very clean.

 

[halzucati]

Ok, I'll try that. I take it your S7 has never done that?
Also, if its decarbing, then what's up with the hardness?

I guess I won't know the difference till I change the process and see...

I mean I'm testing every finished product, huh... hard to believe they could get tougher or more damage resistant... but if they can. I certainly want that.
Unless they get less tough with more carbon... in which case I should see them start snapping.
Interesting. I'll get some foil and see what happens.

Thanks!
- Hal Zucati

 

[Stacy E. Apelt - Bladesmith]

The steel will be the same toughness and hardness. What will change is the surface will be less decarbed and require much less post-HT work.

 

[halzucati]

Just so you can see what I'm talking about:


12" GL.XII post heat treat with natural finish:

Same 12" GL.XII finish ground with all post heat treat finish* removed (*should I call this scale?)

Production example of the 12" GL.XII with the post heat treat scale left on the bevels and edges.
Am I correct in thinking this oxidized/scale finish will provide some rust protection? Or will it just be black?

Thanks for the info and your time.

- Hal Zucati