Comparative Austempering Response Between Weld Metals of ADI Weldments With and Without Cerium Addition

摘要

Austempered ductile iron (ADI) with ausferrite structure is now of great interest for its low production cost, good recycling capacity, excellent castability and a wide range of mechanical properties. However, for more design flexibility and more use of low-cost potential material as well as for repairing the casting defects in producing ADI, the importance of welding DI which could be later converted to ADI, cannot be overridden. In the present work, coated electrode was first developed for grade I ADI without and with cerium using nano-CeO_2 and weld procedure was established as per AWS (D11) using preheat at 300 °C for 1 h followed by post-weld heat treatment (PWHT) for 300 °C for 1 h immediate after welding. DI weldments were then austenitized at 900 °C for 2 h holding time followed by austempering at 300 and 350 °C for three different holding times (1.5, 2 and 2.5 h) at each austempering temperature. Results show that both the weld metals responded austempering heat treatment; but more refined bainitic ferrite and increase volume percentage of retained austenite were obtained in Ce containing weld metal compared to without Ce containing weld metal. Though 100% joint efficiency was observed in both the welded joints (with and without Ce), fatigue strength and charpy impact toughness of ADI weld metals enhanced with the addition of Ce.