Microstructural characteristics of Al-alloyed austempered ductile irons

Microstructural development after austempering ductile irons containing 0.48% and 4.88%Al has been studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental irons were made by green sand casting and gravity die casting. After austenitising at 920 °C for 90 min, an austempering treatment at 400 °C for times up to 100 min resulted in microstructures consisting of carbide-free bainitic ferrite with considerable amounts of high carbon retained austenite.