In this work, the kinetics o f the boride layers (FeB/Fe2B), formed on the X200CrMoV12 steel used fo r the cold-working, was investigated. The bonding treatment was carried out in the powder mixture consisting o f 5%B,C, 5% NaBF. and 90% SiC. The bonding parameters are : 900, 950 and 1000°C with treatment times o f 2, 4 and 6 h. The obtained bonded layers (FeB/Fe,B) were characterized by the following experimental techniques: optical microscopy, scanning electron microscopy coupled to EDS analysis and XRD analysis. The kinetics o f boron diffusion in the X200CrMoV12 steel was also studied. As a result, the time dependence o f the bonded layers thicknesses followed a growth parabolic law. The boron activation energy was estimated as 199.37 kJ m ol' for the X200CrMoV12 steel. A full factorial design with 2 factors at 3 levels was employed to estimate the total boride layer thickness as a function o f the bonding parameters (time and temperature) and a simple equation was proposed. Finally, an iso-thickness diagram was given as a tool to predict the total boride layers thicknesses in relation with the practical utilization o f this kind o f steel.

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