case-harden

verb (used with object)

1. Metallurgy. to make the outside surface of (an alloy having an iron base) hard by carburizing and heat treatment, leaving the interior tough and ductile.
2. to harden in spirit so as to render insensible or insensitive to external impressions or influences; make callous.

verb (tr)

1. metallurgy to form a hard surface layer of high carbon content on (a steel component) by heating in a carburizing environment with subsequent quenching or heat treatment
2. to harden the spirit or disposition of; make callousexperience had case-hardened the judge