Hadn't looked at a Marble's blade in several years, since they first started getting back into the business again, so I went to their website
www.marblesoutdoors.com to see what a changed. A Lot has:
When marbles got back into the business they were manufacturing a couple of their classic older models in, I believe, 5160 and then 52100 carbon steels. Both are excellant steels, with 52100 having the best
reputation for edgeholding of the two. 5160 is seriously tough, used for car/truck springs. I was a little dissapointed in the crudness, only word I can think of, of their grinding for the price they were going for. For that much they could have ground at least to 220, which the ones I looked at didn't seem to be.
In the current classic series, the steel is 0170-6, a prorietery steel first used by Ontario Knife Co in their Bagwell Bowie knifes. Apparently it's no longer proprietery, since Marbles is also using it. Have never tried it, but it's supposed to be a really outstanding carbon steel from what I've read.
Their New Saf-T-Grip series is made with 420 stainless with a rockwell of 54-56. There are actually around 10 different steels out there called 420, that range from being barely steel(.04 carbon) to barely suitable(.50 carbon). It's extremely popular with the factory knife crowd because it's cheap, and easy to work with, you get more dollar profit for your work out of it. My personal opinion is all 420 is junk, but that's from a custom knifemaker's point of view, and in our view(I think I can speak for a lot of us on this) the steel is the soul of the knife.
Their Safety Folder is made using Aus-8 stainless which is a good steel roughly equilant to our 440B, but with a bit of Vanadium, which makes it a better steel.
I didn't bother looking to closely at any of the knives, but you should check to see if the one you're (maybe) buying is convex ground all the way to the edge. The original Marbles Classics were ground that way. This means there was no "normal" edge bevel to sharpen. The proper way to sharpen them was to strop them backwards like a razor. They may have changed that grind, I don't know. Check out their site, that data might be there.
Hope this helps