# On the Effect of Filling Rate on Positive Macrosegregation Patterns in Large Size Cast Steel [PERSON]
## 3 Results and Discussions  
### General Macrosegregation Patterns  
The chemical distribution patterns of the principal alloying elements on the axial plane in the two ingots are shown in Figure 1. The observed section is illustrated in grey in the upper right corner of the figure. The patterns on the left are for LFR and those on the right are for HFR. Regions with no segregation (\(R_{i}=0\)) are colored with light blue, negative segregation (\(R_{i}<0\)) with dark blue, and the hot-top/casting body separation position is marked with a black dashed line. It can be seen that all the solute segregation ratio maps appear symmetric about the ingot central axis, even though minor differences are present. A gradient in solute concentration is observed over the ingot's radius from the periphery to the center and from the lower to the upper region. This indicates that the slow rise in concentration of solute in the solid was the result of bulk liquid becoming progressively concentrated in solute elements.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**C** & **Mn** & **Cr** & **P** & **S** & **Si** & **Ni** & **Mo** & **Fe** \\ \hline
0.36 & 0.85 & 1.82 & 0.01 & 0.0023 & 0.4 & 0.16 & 0.45 & balance \\ \hline \hline \end{tabular}
\end{table}
Table 1: Nominal chemical composition of the investigated steel ingots, wt.%.  
A weak difference from nominal composition (negative segregation) is observed in the region next to the surface layer of the hot-tops. This difference could be attributed to the increased local solidification time due to the presence of the refractory lining in the hot-top wall. The presence of the refractory lining decreases the cooling rate, as compared to the mold wall, and therefore reduces the segregation in these regions [18]. On top of this, some concentration islands were observed, which can be associated with possible segregation channels.  
It is also noted in Figure 1 that segregation features in the two ingots were found to vary as a function of alloying elements. Carbon is the element with the highest segregation ratio. The most intense positive segregation ratio of carbon, manganese, and chromium in both ingots was found to be sequenced in decreasing order, and reached 1.316, 0.225, and 0.212, respectively. The above sequence is consistent with the descending order of the solid-liquid partition coefficient \(k\) (the ratio of the solute content in the solid \(C_{S}\) compared to the solute content in the liquid \(C_{L}\) in equilibrium, \(k=C_{S}/C_{L}\)) of each solute. This coefficient was determined for each element based on linearized binary phase diagrams, with respect to iron calculated using Thermo-Calc(r) (Thermo-Calc Software, Pittsburgh, PA, USA) [16], and the results are shown in Figure 2a. The smaller the partition coefficient of a solute element, the more solute the solid will reject into the liquid during solidification, and the more intense  
Figure 1: Segregation ratio patterns in the two ingots (LFR (Low Filling Rate ingot) and HFR (High Filling Rate ingot)) for the three analyzed solutes: (**a**,**b**) C; (**c**,**d**) Mn; (**e**,**f**) Cr.  
the resulting segregation will be [20]. Although the \(k\) value of manganese lies between carbon and chromium, as seen in Figure 2a, its slightly lower diffusion coefficient in the liquid iron (as displayed in Figure 2b [21]) results in a similar positive segregation pattern to chromium. In addition, as shown in Figure 1, the most intense segregations of all the solutes (the red color in the maps) in LFR were observed at the top center of the hot-top, in contrast to the lower locations of positive segregates of manganese and chromium in HFR.