Influence of molybdenum on austempering behaviour of ductile iron Part 2 – Influence of austenitising temperature on austempering kinetics,mechanical properties,and hardenability of ductile iron containing 0·13%Mo

Abstract

Austempering kinetic and mechanical property measurements are reported for austenitising temperatures of 950, 920, 870, and 840°C and an austempering temperature of 400°C for an iron of composition Fe–3·51C–2·81Si–0·25Mn–0·39Cu–0·13Mo– 0·04Mg. Increasing the austenitising temperature to improve the hardenability also narrows the heat treatment processing window but does not close it. Mechanical property measurements show that the ASTM Standard A897 : 1990 for ADI is satisfied using austenitising temperatures of 920, 870, and 840°C but the tensile properties just fail to satisfy the standard for an austenitising temperature of 950°C. This is attributed to the fact that the definition of the processing window does not allow for mechanical instability of the ausferrite structure. The properties satisfy the new European ADI standard BS EN 1564 : 1997 for all four austenitising temperatures.