Investigation of effect of austempering heat treatment on mechanical properties of en GJS 650 ferritic spherical cast irons

The aim of this study was to investigate the influence of austempering on the mechanical properties of solution-strengthened ferritic cast ductile irons. The mold was formed in a Y-shaped geometry corresponding to ASTM A571M. The microstructural examinations of the samples were conducted using optical microscopy, scanning electron microscopy, and X-ray diffraction. Hardness, impact, and tensile tests were performed to determine the mechanical features. After the impact test, the fracture surface morphology was analyzed with scanning electron microscopy. The austempering results showed that the matrix structure with 70% ferrite and 30% bainite had the highest fracture toughness and yield strength. The ausferrite phase in microstructure played a positive role in ductility, toughness, and strain rates. The mechanical properties were strongly related to the amounts of ausferrite and retained ferrite ratio. Production of SSF-DI at industrial scale leads to price savings owing to decreased machining costs. Austempered SSF-DI materials have a relatively high yield strength and elongation at failure, depending on the matrix of soft ferritic structure. Heat treatments cause an increase in strength, so ductility decreases because of the structure of the bainite. The silicon content in the microstructure restricts the iron carbide formation in as-cast DI, but it increases the solid solution strengthening. In addition to good yield strength, the other advantages can also be aligned as very good machinability. The present study focused on investigating the influence of austempering parameters on microhardness, toughness features, and tensile strength of solid solution-strengthened ferritic (SSF)-DI.