Characterization and boriding kinetics of C38 carbon steel: effect of the process time

Abstract

This present work investigates the effect of the time duration on the boriding kinetics of C38 steel. The pack-boriding treatment was carried out at 1000 °C for 0.5, 1, 2, 4 and 8 h using a powdery mixture consisting of 5%B4 C, 5%NaBF4 and 90% SiC. The boride layers were characterized by the following experimental techniques: (Scanning electron microscopy, X-ray diffraction analysis, Vickers microhardness tester and measurement of the mass gain). The observations by scanning electron microscope revealed that the Fe2 B layer was formed after a short time (0.5 or 1 h). The boride layers were composed of FeB and Fe2 B phases for a treatment time exceeding 2 h. The surface roughness of the borided samples was increased with the boriding time. The mass gain due to the boriding was investigated and its evolution was described by a parabolic law. In addition, the experimental boride layers thicknesses were compared to those predicted by the diffusion model. A good agreement was obtained between the simulation results and the experimental data. Finally, contour plots that describe the evolution of the boride layers formed on the borided C38 steel were established. The iso-thickness diagrams can be used as a tool to select the boride layer thickness in relation with its practical use.