Influence of molybdenum on austempering behaviour of ductile iron Part 1 – Austempering kinetics and mechanical properties of ductile iron containing 0·13%Mo

Abstract

Measurements of the austempering kinetics and mechanical properties are presented for a ductile iron of composition Fe–3·51C– 2·81Si–0·25Mn–0·39Cu–0·13Mo–0·04Mg (wt-%) for austempering temperatures of 285, 320, 375, and 400°C after austenitising at 870°C for 120 min. The kinetic studies show that the alloying level is insufficient to cause a significant delay in ausferrite formation in the intercellular boundaries. This implies that the heat treatment processing window is open for all austempering conditions studied. The mechanical property measurements show that with the correct selection of austempering temperature all the grades of the ASTM Standard 897M : 1990 and BS EN 1564 : 1997 can be satisfied. The hardenability of the present iron is limited and it is therefore unlikely that these standards will be achieved in thicker section components.