1985 Volume 26 Issue 4 Pages 236-241
Plane and rotating bending fatigue tests of boronized steels with various thicknesses of boronized layers were conducted. The effect of the thickness of boronized layer on the crack initiation and propagation mechanism was investigated by fatigue crack observation. Many cracks propagating perpendicular to the tensile axis and those propagating parallel to it with connecting each other to spall the boronized layer, were observed. Fatigue cracks were observed also in a specimen which was not fractured up to the cyclic number 107. But all those cracks were arrested either in the boronized layer or in a boundary between the boronized layer and the matrix. Fracture was controlled by whether the crack propagated through the boundary or not. Fatigue strength of boronized specimens with Fe2B uni-layer was higher than that of boronized specimens with FeB+Fe2B bi-layer. The maximun fatigue strength was obtained, when the volume of Fe2B layer was controlled so as to be about 1.5% of the total volume.
