In this study, the growth kinetics of the boride layers forming on low carbon steel substrates was investigated during electrochemical boriding which was performed at a constant current density of 200 mA/cm(2) in a borax based electrolyte at temperatures ranging from 1123K to 1273K for periods of 5-120 min. After boriding, the presence of both FeB and Fe(2)B phases were confirmed by the X-ray diffraction method. Cross-sectional microscopy revealed a very dense and thick morphology for both boride phases. Micro hardness testing of the borided steel samples showed a significant increase in the hardness of the borided surfaces (i.e., up to (1700 +/- 200) HV), while the hardness of un-borided steel samples was approximately (200 +/- 20) HV. Systematic studies over a wide range of boriding time and temperature confirmed that the rate of the boride layer formation is strongly dependent on boriding duration and has a parabolic character. The activation energy of boride layer growth for electrochemical boriding was determined as (172.75 +/- 8.6) kJ/mol. (C) 2011 Elsevier B. V. All rights reserved.