The relationship between inclusion clustering and embrittlement of ferritic spheroidal graphite cast iron at intermediate low temperatures

Four fully annealed ferritic spheroidal graphite cast irons with different carbon equivalents were used to perform tensile tests at temperatures ranging between -120°C and 40°C. In addition, all the materials were electro-chemically etched in Morries solution to reveal the distribution morphologies of inclusion particles and thus to explore the influence of inclusion clustering on low temperature tensile properties. The experiment results indicate that elongation deteriorates at a temperature of around -30°C. This phenomenon is known as intermediate low temperature embrittlement. At this temperature the fracture surface shows a part ductile/partial brittle pattern. We can see that brittle cracks start at the clustering region of the inclusion particles, at the zoned brittle fracture area. Our electro-chemical etching results demonstrated that the specimens with a lower CE value exhibited greater inclusion particle clustering at the eutectic cell walls. Furthermore, the degree of inclusion clustering significantly affected the intermediate low temperature embrittlement of the ferritic SG cast iron. For the materials with a lower carbon content that possess a denser clustering of inclusion particles, the elongation drop was more obvious. It is worth noticing that the inclusion particles are more uniformly distributed in the higher CE materials which will lower the probability of crack initiation and thus the elongation drop is reduced.