They are quenched and tempered steels with a chemical composition that has an addition of aluminium, chromium, molybdenum, vanadium. In contact with nitrogen they form hard nitrides.
They have an excellent wear resistance and abrasion resistance, combined with an improvement in corrosion resistance in aggressive environments. For all these characteristics they are preferred over case-hardening steels, but also for the low number of deformations that come from the nitriding treatment.
Jominy hardenability demonstrates that they are steels with an excellent hardenability, some are tougher, for example 34CRALMO7, whereas 41CRALMO7 has an excellent superficial hardness.
For what concerns reliability and functionality, you can obtain a hardened superficial layer that can vary from 0,05 yo 1 mm, considering an increase in the fragility related to the nitriding thickness.
Hardness that you obtain from the nitriding heat treatment is more elevated than the one you obtain from case-hardening steels and hardened steels.