This article firstly presents results for C45 steel surface modification by post boronizing N+ ion implantation. One boronizing technique, gaseous boronizing with solid boron-yielding agents (GBSA), was employed to make C45 steel boronizing. SEM, XRD, AES, Vicker's microhardness tester and potential dynamic electrochemical were employed to characterize the samples. The properties of the boride layer of C45 steel can be improved by use of post boronizing ion implantation. c-BN compounds can be formed in the boride layer after N+ ion implantation. (C) 2002 Elsevier Science B.V. All rights reserved.