Wish we could know if the factory corrected the mistake on the first hammers. If they fixed the problem messing with them now would not improve anything. I guess I would compare the hardness of the new ones by filing on an out of sight area. If the replacements are no harder, what to do with an unknown steel is a problem.
If a spark test maybe on one of the old ones might indicate the carbon content. If it is low carbon steel case hardening may improve things.
These 2 recent threads in a machinist forum maybe helpful:
https://www.practicalmachinist.com/vb/gu...ccesses-384163/https://www.practicalmachinist.com/vb/ge...estions-383361/In the past I have sent tools out rather than mess with case hardening. Even with an oven now I still have sent case hardening work out.
