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 (alpha(B)), which develops during continuous cooling as a coarse, feathery-type structure within the prior austenite (gamma) grains. Regardless of alloy composition, the ausfertite that forms in the microstructure during casting in volume fractions greater than similar to0. 1 was found to have a constant bainitic ferrite/retained austenite ratio (alpha(B/gamma)similar to3). Electron backscatter diffraction (EBSD) in the scanning electron microscope has demonstrated that alpha(B) and gamma in ausferrite is related by the Kurdjumov-Sachs orientation relationship: {111} gamma//{011}(alpha) and <011<gamma//<111>, with a number of alpha(B) variants possible within a given austenite grain. This study confirms that the ausferrite generated in gray iron by direct casting has comparable micro structural and crystallographic characteristics to that produced in austempered gray and ductile irons. (C) 2004 Elsevier Inc. All rights reserved.