simple past tense and past participle of case harden

(metallurgy) Metal that is harder at its surface, due to a case hardening process.

Alternative spelling of case hardened / Hardened by experience.

(metallurgy) The repeated plastic deformation of a material, causing a permanent distortion of its crystal structure, and an increase in its strength

(metallurgy) Designating, or pertaining 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.

(of metal) Age hardening; a heat treatment technique to increase the yield strength of malleable materials.

to cold-hammer

(literally and figuratively) Unfeeling or lacking emotion due to experience in battle; callous.

(idiomatic, usually reflexive, dated) To make someone more resistant to something.

(obsolete) To grow more obstinate.