Analysis of ductile cast iron tensile tests to relate ductility variation to casting defects and material microstructure

This paper describes an experimental and analytical study to correlate the ductility variation in ductile cast iron to casting defects and the cast iron's microstructure. A large set of specimens from three manufactured components were tested to derive statistical distributions of tensile and fracture properties. Eighty-one of 150 tested tensile specimens were analyzed by metallography and fractography to identify and size defects and microstructural variations. It was found that the elongation at fracture was reduced by casting defects in the form of magnesium-oxide films and to a lesser extent by the graphite properties and pearlite content. The paper presents an elastic–plastic probabilistic fracture mechanics model that relates the variation in ductility to the size and shape of casting defects. The agreement between computed and measured results is quite good.