# On the Effect of Filling Rate on Positive Macrosegregation Patterns in Large Size Cast Steel [PERSON]
## 2 Materials and Experimental Process  
Two 40 metric ton (MT) cylindrical shape steel ingots, 250 cm in height and 150 cm in mean diameter, were cast in big-end-up cast iron molds using identical conditions, except for the filling rate. The hot-top, as an extension of the ingot that was 70 cm in height, was made in the mold lined inside with insulating tiles. During the production process, molten steel with the nominal composition listed in Table 1 was first produced by melting scrap material in an electric arc furnace, and then teemed into a ladle before ladle refining and vacuum degassing in an argon atmosphere. Then it was smoothly bottom poured into the mold at 1570 \({}^{\circ}\)C, until the mold was filled to the top of the insulating tiles. Two filling times were used: the first ingot named LFR (Low Filling Rate ingot), with a filling rate of about 0.0018 m/s (30 min for the 40 MT ingot), and the second one, HFR (High Filling Rate ingot), with a filling rate of about 0.0024 m/s (22 min). The liquidus temperature for the current material was determined to be 1495 \({}^{\circ}\)C, using the thermodynamic software Thermo-Calc(tm) (Thermo-Calc Software,Pittsburgh, PA, USA) [16]. Based on this value, the initial superheat (the excess temperature above the melting point) for both ingots was determined to be 75 \({}^{\circ}\)C.  
After solidification, a block comprised of the hot-top and 30 cm thick section of the ingot's main body was transversely cut off for investigation. Then, two plates (130 \(\times\) 70 \(\times\) 1.5 cm\({}^{3}\)) were sliced on each side of the axial plane. One slice was sectioned at regularly-spaced intervals into over 250 samples (6.5 \(\times\) 4.5 \(\times\) 1.5 cm\({}^{3}\)). All the faces in the centerline plane along the longitudinal axis were ground, and then chemically mapped using the Thermo Scientific the ARLTM 4460 Optical Emission Spectrometer (Thermo Fisher Scientific Inc., Waltham, MA, USA). The axial face of the other slice was prepared by grinding and macroetched in a 50% HCl solution at 50 \({}^{\circ}\)C to reveal macrosegregation patterns. Some selected regions were metallographically prepared and etched in Oberhoffer's etchant, and then optically observed using a binocular microscope.  
It should be noted that hot-tops are commonly used in the ingot casting industry in order to provide a reservoir of molten steel for feeding the shrinkage zone as the ingot solidifies [1]. They are generally cut off from the ingot body after solidification. However, there is a growing interest in reserving at least part of the hot-top for further use [17]. Thus, in the present study, positive segregation in the hot-top was also characterized, along with the upper section of the casting body, to evaluate and validate such possibility. It is clear that, if successful, the findings could result in significant material and energy saving in the ingot casting industry.  
The chemical composition of each specimen was obtained by averaging out 3 random spectrometer measurements and calculated using the relation [18]:  
\[R_{i}=(\omega_{i}-\omega_{0,i})/\omega_{0,i},\]  
Here, \(R_{i}\) is the segregation ratio for solute element \(i\), \(\omega_{i}\) is the solute's local concentration and \(\omega_{0,i}\) is its nominal concentration value. A positive \(R_{i}\) value corresponds to positive segregation, and conversely, a negative \(R_{i}\) to negative segregation. Segregation ratio patterns of different elements in the longitudinal section of the entire block were then reconstructed using MATLAB(r) (The MathWorks Inc., Natick, MA, USA) [19] by filling the areas between the isolines using constant colors corresponding to the local segregation intensities.