"Fully hardened steel" is "very resistant" to galling, not immune from galling especially if it is rough. At least in the 30 years I've been a machinist it's been that way. The only parts of a firearm that are fully hardened are usually "case hardened" which hardens a shallow depth of the steel and is used to color parts for rust resistance ( it is impervious) or to harden sear surfaces. Most firearms are fairly soft so nothing cracks.
