It has been shown by several researchers that the hardness of a Cr-C deposit obtained from a trivalent Cr-based bath can be tremendously increased to be 1600 Hv after annealing at 600 degrees C for 1 h. Presently the precipitation of fine chromium carbides in the annealed Cr-C deposit is considered to be the hardening mechanism. However, based on our experimental data, we find that precipitation of a nanosized diamond-structured membrane could be the main hardening mechanism. According to this alternative hardening mechanism, hardening of a Cr-C deposited steel can be accomplished with induction- and flame-heating within a 1 s time period. (C) 2009 Elsevier B.V. All rights reserved.