Microstructure and tribological performance of boride layers on ductile cast iron under dry sliding conditions

Abstract

Stamping die is prone to wear failure due to mechanical friction. In this work, high-hardness boride layers were obtained on ductile cast iron as stamping die, by a boronizing process at 800–950 ℃ for 2–6 h with the addition of rare-earth oxide La2O3. A sawtooth-like morphology of the boride layer was observed using scanning electron microscopy (SEM). The greatest boride layer micro-hardness of the boride layers of 1648 HV0.1 was obtained at 900 ℃ and 6 h with 4% La2O3, and X-ray diffraction (XRD) analysis showed that the boride layers were a component of Fe2B as adding La2O3. The tribological tests showed that the wear resistance of the boride layers was enhanced with increasing boronizing temperature and time, where the ductile cast iron substrate corresponding to 900 ℃ and 6 h exhibited the best wear resistance. Compared with that of the boride layer without La2O3, the thickness and wear resistance of the boride layer with 4% La2O3 was increased by 37.2% and 31%, respectively. The thickness of the boride with 6% La2O3 decreased by 27.6%, and the wear rate was highest, indicating that excessive La2O3 inhibited the enhancement effect. The wear mechanism of the boride layers transformed from mild adhesive wear to fatigue spalling as the normal load and sliding speed increased.