from
The Collaborative International Dictionary of English v.0.48
Self-hardening \Self`-hard"en*ing\, a. (Metal.)
Designating, or pert. to, any of various steels that harden
when heated to above a red heat and cooled in air, usually in
a blast of cold air with moderate rapidity, without
quenching. Such steels are alloys of iron and carbon with
manganese, tungsten and manganese, chromium, molybdenum and
manganese, etc. They are chiefly used as high-speed steels.
-- {Self`-hard"en*ed}, a.
[Webster 1913 Suppl.]