Refinement of As-cast Austenite Grain in Carbon Steel by Addition of Titanium

Effects of Ti addition on as-cast austenite structure of S45C steel have been investigated by means of furnace cooling experiment at a cooling rate of 0.03°C/s, focusing on the Ti addition ranging from 0 to 0.5 mol%. The Ti addition reduces average austenite grain diameter down to a size comparable to secondary dendrite arm spacing. In samples with the Ti addition, the austenite grain boundary is located at inter-dendritic position where Ti(C,N) particles exist and the refinement of austenite grain structure is ascribable to pinning effect of the Ti(C,N) particle formed in L+γ-Fe+Ti(C,N) phase field. The increment of Ti addition does not substantially change the size of Ti(C,N) particle but increases the number of the Ti(C,N) particles, leading to further refinement of the austenite grains