EN H320 LA steel sheets were boronized with four different boron sources (Ekabor 1, Ekabor 2, Ekabor 3 and Ekabor HM) by the powder pack method. The boronizing process was carried out at 973, 1 073 and 1 173 K for 3 h. The bonded samples were investigated by means of X-ray diffraction, optical microscopy, microhardness measurements and tensile tests. XRD studies showed that the boride layer consisted of phases FeB and Fe2B. The microhardness of the boride layers ranged between 1 450 and 1 651 HV, depending on the boronizing source. The thickness of the boride layer increased with increasing particle size of the boronizing powders and with increasing boronizing temperature. Tensile properties were also affected by the boronizing process and the particle size of the boronizing powders. Microhardness, tensile strength and elongation values were improved with the boronizing treatment. Extensive cracking was observed at the interface between the Fe2B and FeB layers.