Fracture toughness of borides formed on boronized ductile iron

In this study, fracture toughness properties of boronized ductile iron were investigated. Boronizing was realized in a salt bath consisting of borax, boric acid and ferro-silicon. Boronizing heat treatment was carried out between 850 and 950 °C under the atmospheric pressure for 2–8 h. Borides e.g. FeB, Fe2B formed on ductile iron was verified by X-ray diffraction (XRD) analysis, SEM and optical microscope. Experimental results revealed that longer boronizing time resulted in thicker boride layers. Optical microscope cross-sectional observation of borided layers showed dentricular morphology. Both microhardness and fracture toughness of borided surfaces were measured via Vickers indenter. The harnesses of borides formed on the ductile iron were in the range of 1160–2140 HV0.1 and fracture toughness were in the range of 2.19–4.47 MPa m1/2 depending on boronizing time and temperature.