Further informations. It doesn't works on rings too. Anyway if after the enchantment in your tool tip object you see: Offense slot: +50 Critical strike and Armor Penetration, it works. If you see Equip: +50 Critical strike and Armor Penetration, it doesn't works.
I Have the same problem with savage enchantment. It shows the effect if I put it on a weapon (offense slot +crit and ap) but not if I put on the belt or the neck (still offense slot). Rank 3 and 4 here.