Microstructural and crystallographic features of ausferrite in as-cast gray iron

Ausferrite has been shown to form during casting of gray iron by carefully controlling the alloying additions Mo, Mn, Si and Cu and consists of an acicular ferrite constituent, termed bainitic ferrite (αB), which develops during continuous cooling as a coarse, feathery-type structure within the prior austenite (γ) grains. Regardless of alloy composition, the ausferrite that forms in the microstructure during casting in volume fractions greater than ∼0.1 was found to have a constant bainitic ferrite/retained austenite ratio (αB/γ∼3). Electron backscatter diffraction (EBSD) in the scanning electron microscope has demonstrated that αB and γ in ausferrite is related by the Kurdjumov–Sachs orientation relationship: {111}γ//{011}α and <011>γ//<111>α with a number of αB variants possible within a given austenite grain. This study confirms that the ausferrite generated in gray iron by direct casting has comparable microstructural and crystallographic characteristics to that produced in austempered gray and ductile irons.