This study evaluates the fracture toughness of Fe2B boride layers formed by the paste boriding thermochemical process on an AISI 1018 steel surface. The samples were placed in acrylic molds for the impregnation of boron carbide paste with thickness of 4mm over the sample surfaces to produce the diffusion into the steel. The aforementioned treatment considered one temperature, T= 1273 K, and three exposure times t=5, 6 and 8 h. Later, the borided samples were prepared metallographically to determine the mean values of the layer thicknesses and to produce Vickers microindentations at 45 m from the surface, applying four loads (1.9, 2.9, 4.9 and 9.8 N). The microcracks generated at the corners of the Vickers microindentation were considered as experimental parameters, which are introduced into two Palmqvist cracks models to determine their corresponding fracture toughness KC. As a result, the experimental parameters, such as exposure time and applied load are compared with the resulting fracture toughness of the borided phase.