de·ca·les·cence 
(dē′kə-lĕsəns)
(dē′kə-lĕsəns)n.
A sudden slowing in the rate of temperature increase in a metal being heated, caused by endothermic structural changes and resulting in a darkening of the metal.
[From DE- + Latin calēscere, to become warm, inchoative of calēre, to be warm; see kelə-1 in the Appendix of Indo-European roots.]
de′ca·lescent adj.