AbstractTh e effect of silicon on the microstructure and solidification segregation of directionally solidified IN738 nickel-based superalloy was studied. Directional solidification at various solidification rates and partial directional solidification plus rapid quenching were applied. Metallographican alysis and an electron microp robe were mainly used to observe and measure the micro structure and elemental segregation of the alloy, respectively. It was found that silicon affected the morphology of the liquid-solid interface of the alloy during solidification and gave the alloy a tendency to form well-developed dendrites. The addition of siliconen larged the solid us-liquidus temperature interval. and the solidification rate also greatly influenced the interval. The interval increased with increasing solidification rate. Silicon promoted the precipitation of theγ/γ' eutectic, and also affected its precipit ation temperature. Silicon segregated mainly in interd endritic regions, and promoted the segregation of other elements. All of the effects of silicon on the alloy related to the solidification rate.