Effect of (Fe,Cr)7C3 carbide orientation on abrasion wear resistance and fracture toughness

In this study two white cast irons with different chromium contents 13.81% and 24.41% were solidified unidirectionally. Their microstructures are composed of oriented M7C3 carbides and eutectic matrices. The specimens were cut parallel and transversally to the billet axe and pin-abrasion tests were carried out using fixed alumina abrasive grains. The microhardness, elastic modulus and fracture toughness were determined using an indentation technique on transversal and longitudinal sections of the M7C3 carbides. M7C3 carbides show higher microhardness in transverse than in longitudinal direction. Longitudinal M7C3 carbides show higher fracture toughness in the direction perpendicular to the larger edge of the carbide than either parallel to the larger edge or on the transverse section. The results reveal that the white cast iron presents higher abrasion resistance in transverse section than in longitudinal section of the M7C3 carbides. The wear surface was examined by scanning electron microscopy for identifying the wear micromechanisms and was correlated with the fracture toughness of the carbides. The results show that when the carbides fracture, the cracks propagate parallelly to the larger edge of the M7C3, the direction where the fracture toughness is lower.