Effects of Addition of Titanium and Boron on Columnar Austenite Grain in Carbon Steel

We performed casting experiment of S45C steel, focusing on the effect of addition of Ti and B on as-cast austenite grain structure. Without the addition of these elements, the austenite structure consists of columnar grains over the whole sample in the present casting conditions. The addition of Ti and B leads to the formation of equiaxed austenite grains and, importantly, fully equiaxed austenite structure was observed in the sample with 0.2 mol% Ti and 0.4 mol % B. The microstructural observations indicated that this behavior of austenite structure stems from the columnar-to-equiaxed transition of ferrite dendrite structure. The addition of these elements, furthermore, leads to refinement of the columnar austenite grain