Abnormal Analysis on Fracture of QT500-7 Ductile Iron Tensile Specimen

In the tensile test, the fracture surface of QT500-7 ductile iron tensile specimen had dark abnormal area on the fractured specimen. The causes of the abnormal area were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination and mechanical property test. The results show that there were a lot of vermicular graphite in the microstructure of ductile iron caused by the poor spheroidization or the degradation of spheroidization during the casting process, which led to the abnormal fracture of ductile iron tensile specimen, which seriously reduced the mechanical properties of ductile iron such as yield strength, tensile strength and elongation after fracture.