Abstract Some properties such as hardness and fracture toughness of boride formed on the 99.97 wt% pure iron were investigated. Boronizing was carried out in a solid medium, consisting of Ekabor powders of 5% B4C as donor, 5% KBF4 as an activator and 90% SiC as diluent at 800 °C for 2, 4 and 8 h. The dominant phase formed on the substrate was found to be Fe2B that had a finger-like shape morphology. The hardness of boride on the 99.97% pure iron was over 1700HVN, while the hardness of pure iron was about 130HVN. It was found that the fracture toughness of boride formed on surfaces of 99.97% pure iron, depending on the process time, ranged from 3.59 to 3.83 MPa m1/2. Depending on process time and temperature, the depth of the boride layer ranges from 22 to 43 μm, leading to a diffusion-controlled process.