The solidification structure and properties of P-B cast irons

A series of P-B cast irons are quenched during solidification to evaluate the partition coefficient of P sohdification to evaluate the partition coefficient of P and B to austenite (kP and kB) and to reveal the crystallization sequence. The thermal analysis shows that the solidification proceeds in the order of primary austenite (gamma), gamma+graphite eutectic and steadite, The IMA analysis reveals that the kP and kB are about 0.15 and 0.05 respectively, and the B promotes the crystallization of plate-like cementite Fe-3(CB) in steadite. The microstructure and tensile properties of P-B cast iron solidified in sand molds with and without chill blocks were also studied with a result showing that the chill blocks refine the solidification structure, but they reduce the tensile strength. This is attributed to the higher temperature gradient which would make the eutectic graphite crystallize in deleterious shape and distribution.