Abstract: Precipitation and nucleation of TiN during solidification of clean steel have been studied. And the possibility of using TIN to refine as-cast grains as heterogeneous nucleation sites as well as to reduce mac-rosegregation in continuous casting of steel is discussed. The conditions that TiN precipitates at the beginning of solidification have been acquired and the effectiveness of this TiN refining as-cast structure process has been investigated with comparative experimental methods. It is shown that refining grains by inoculating clean steel with TiN is an effective way provided that the process is controlled strictly.