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tr.v. face-hard·ened, face-hard·en·ing, face-hard·ens
To harden the surface of (a metal).
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Metallurgy) (tr) to harden the surface of (steel or iron) by the addition of carbon at high temperature
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
Past participle: face-hardened
Collins English Verb Tables © HarperCollins Publishers 2011