carburize

verb (used with object), car·bu·rized, car·bu·riz·ing.

1. to cause to unite with carbon.
2. to carburet.

verb

1. another word for carbonize (def. 2), carbonize (def. 3)
2. (tr) to increase the carbon content of (the surface of a low-carbon steel) so that the surface can be hardened by heat treatment