Growth of boride layers on the 13% Cr steel surface in a mixture of amorphous boron and KBF₄

Two borides FeB and Fe₂B were found to form as separate layers at the interface between a 13% Cr steel and boron at 850–950 °C and reaction times up to 12 h. The average chromium content is 8 at.% in the FeB layer and 9 at.% in the Fe₂B layer. Both layers are characterized by a pronounced texture. The strongest reflections are {002} and {020} for the orthorhombic FeB phase and {002} for the tetragonal Fe₂B phase. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data. Annealing of a borided steel sample in the absence of boriding media results in disappearance of the FeB layer. Microhardness values are 17.9 ± 1.5 GPa for the FeB layer, 16.1 ± 0.9 for the Fe₂B layer and 5.9 ± 0.3 GPa for the steel base. The abrasive wear resistance of the FeB layer is 25 times greater than that of the steel base. The Fe₂B layer yields about a 15-fold increase in wear resistance of steel samples.