Both salt bath and induction heat treatment can be done well or poorly. Induction is generally preferred in mass production, as it's faster and uses less energy. Salt bath has the advantage of being able to treat anything you can fit in the bath, while induction can require part specific coils. Induction also has advantages for differential treatments -- you might want the face of a hammer hardened different than the back, and that's much easier with induction, and you might be able to do both at the same time, which further reduces time and handling requirements.
You can differentially heat treat hammer heads using salt baths.
Usually, the hammer heads are suspended from hooks thru the eye, and each face is separately dipped.
I’ve seen video of it being done, which I thought might have been older video from Vaughan, but maybe Vaughan changed their process, or uses a different process for different head types, or maybe I have the manufacturer wrong.
I think Estwing just dips the entire upper portion of the hammer, above were the handle tang is located.
I know there must be chipped Estwing hammers out there, but I don’t see them much.
I have personally chipped a chunk out of an MOB hammer from France, by hitting the corner of the rectangular face of the hammer on an anvil due to an errant strike.
MOB uses induction hardening from what I recall.
I presume steel differences also might come into play, but that is harder to check for.
hammersource.com
