Effects of Molybdenum and Copper Additions on Microstructure of High Chromium Cast Iron Rolls

To clarify the effect of alloying elements on transformation behavior of destabilization heat treated high chromium cast irons, specimens of high chromium hypoeutectic cast irons containing copper and molybdenum were destabilization heat treated at 900, 1000 and 1100°C for 5×102 to 5×104 sec and then rapidly cooled down to room temperature. As the destabilization heat treatment temperature and soaking time rise, the molybdenum content in the primary dendrite region and the amount of retained austenite are increased, but chromium atoms supersaturated in the primary austenite phase during solidification are precipitated into complex chromium carbides. The presence of copper promotes the attainment of microstructure consisting of discontinuous eutectic carbides. It was observed in the present work that some amount of copper solutes were contained in the secondary carbides precipitated in the copper added cast irons. EDS quantitative analysis showed 5.64% copper. A molybdenum-rich eutectic structure grown in the periphery of eutectic colony appearing a lamellar shape was observed in the 2.8% molybdenum contained cast irons during destabilization heat treatment at 1000°C for 5×102 sec.