Influence of rare earth nanoparticles and inoculants on performance and microstructure of high chromium cast iron

Abstract

The high chromium cast irons (HCCIs) with rare earth (RE) nanoparticles or inoculants were fabricated in the casting process. The phase compositions and microstructure were analyzed by X-ray diffraction (XRD) and optical microscopy (OM), respectively. The hardness and impact toughness were tested by Rockwel-hardmeter and impacting test enginery. And then, the morphology of fracture was researched by scanning electron microscopy (SEM). The results demonstrated that the phase compositions of HCCIs with addition of RE nanoparticles or inoculants which were M7C3 carbides + a-Fe did not change obviously. However, the prime M7C3 carbides morphology had great changes with the increase of RE nanoparticles, which changed from long lath to granular or island shape. When the content of RE nanoparticles was 0.4 wt.%, the microstructure of high chromium cast iron was refined greatly. The microstructure of carbides was coarser when the addition of RE nanoparticles was higher than 0.4 wt.%. The hardness and impact toughness of HCCIs were improved by addition of RE nanoparticles or inoculants. The impact toughness of HCCIs was increased 36.4% with RE nanoparticles of 0.4 wt.%, but the hardness changed slightly. In addition, the adding of RE nanoparticles or inoculants could reduce the degree of the brittle fracture. Fracture never seemed regular, instead, containing lots of laminates and dimples with the increase of the RE nanoparticles. The results also indicated that the optimal addition amount of the RE nanoparticles was 0.4%, under this composition, the microstructure and mechanical property achieved the best cooperation. In addition, through the study of erosion wear rate, when adding 0.4% RE nanoparticles into the HCCIs, the erosion wear rate got the minimum 0.32×10−3 g/mm2, which could increase 51.5% compared with that without any RE nanoparticles.