冶 mainly means to smelt or cast metal: 冶金 (metallurgy), 冶炼 (to smelt). A separate sense, 'alluring, gaudily seductive', appears in 妖冶 and usually carries a slightly disapproving tone.
The ice radical, here used by analogy: just as ice melts into water, metal melts under fire. It is the indexing radical and points to the 'melting' core of 冶.
