The effect of filling velocity on positive macrosegregation in large size steel ingots was studied. Macrosegregation and macro/microstructures were characterized on the hot-tops and a portion of the upper section of two ingots. The measurements revealed that segregation features in the two ingots varied as a function of the alloying elements, and that the severity of positive macrosegregation in the casting body was reduced when the filling rate was increased. It was also found that at the higher filling rate, grain morphologies in the first solidified zones of the ingot changed from columnar to equiaxe, and secondary dendrite arm spacing (SDAS) became slightly smaller in the intermediate and final solidified zones. The experimental findings were analyzed in the framework of diffusion and convection-controlled solidification, as well as liquid metal flow theories. The solute dependence of segregation features was related to the difference in the solid-liquid partition coefficient and diffusion capability of each element in the liquid iron. Calculation of Reynolds numbers (Re) during the filling process, for both ingots, showed that higher filling velocity caused more instable movement of the liquid metal in the initial solidification stage, resulting in the modification of grain morphology, as well as accelerated solidification rate.

Finite element modeling (FEM) validated by experimental work was used to simulate the influence of thermomechanical shrinkage on macrosegregation of alloying elements in a large size ingot of high strength steel. The full algorithms of the filling and solidification process for thermohydraulic and thermomechanic analyses were developed and implemented in the 3D FEM code Thercast ® . Material properties were determined by a combination of experimental works, thermodynamic software Thermo-Calc ® , a database and literature source. It was predicted that thermomechanical shrinkage decreased the temperature gradients, advanced the initiation of solidification and reduced the solidification time. The above changes resulted in less severe segregation along the centerline, in the zone next to the ingot surface, in the upper section of the ingot and in the hot-top. Thermomechanic model predictions were proved to agree better with experimental results than the thermohydraulic one. The obtained results were interpreted in the framework of the theories on diffusion and solidification of alloyed systems. These findings contribute to a better understanding of the impact of thermomechanical shrinkage in ingot cooling process. They could also be used in industry to improve the quality of large size ingot production and the productivity of high value added steels or other alloys.

In the present work, the influence of filling rate on macrosegregation in a 40-Metric Ton (MT) ingot of a high-strength low-carbon steel was studied using finite element (FE) simulation. The modelling of the filling and solidification processes were realized with a two-phase (liquid-solid) multiscale 3D model. The liquid flow induced by the pouring jet, the thermosolutal convection, and the thermomechanical deformation of the solid phase were taken into consideration. Two filling rates were examined, representing the upper and lower manufacturing limits for casting of large size ingots made of high strength steels for applications in energy and transportation industries. The evolution of solute transport, as well as its associated phenomena throughout the filling and cooling stages, were also investigated. It was found that increasing the filling rate reduced macrosegregation intensity in the upper section, along the centerline and in the mid-radius regions of the ingot. The results were analyzed in the framework of heat and mass transfer theories, liquid flow dynamics, and macrosegregation formation mechanisms.

A 3D model was employed to study the effect of melt initial superheat on the macrosegregation formation using FE modeling and experimentation methods. The casting process of three ingots with the initial melt superheats of 75°C, 65°C and 55°C were simulated. The three cases represented three variables encountered in industry during casting of large size ingots. For the above three studied cases, all other casting conditions were kept the same. Results showed that the variation of initial melt superheat gave rise to changes in temperature pattern, liquid flow field, solidification speed, and thermomechanical contraction. Under the combined actions of all these changes, lower superheat tended to alleviate the segregation intensity in the upper part of the ingot body, in the hot-top, and in the solute-rich bands between the ingot centerline and periphery. The beneficial effect of lower superheat on alleviation of segregation severity was confirmed by experimental chemical measurement results. The results were analyzed in terms of heat and mass transfer theories and allow for a better understanding of the underlying mechanisms responsible for the occurrence of macrosegregation in ingot casting process. The findings should be helpful for the casting process design of a given ingot of high value-added steels or other alloys.

The effect of filling velocity on positive macrosegregations in large size steel ingots was studied. Macrosegregation and macro-/micro-structure were characterized on the hot-tops and a portion of the upper section of two ingots. The measurements revealed that segregation features in the two ingots varied as a function of the alloying elements, and that the severity of positive macrosegregation in the casting body was reduced when the filling rate was increased. It was also found that at the higher filling rate, grain morphologies in the first solidified zones of the ingot changed from columnar to equiaxe, and secondary dendrite arm spacing (SDAS) became slightly smaller in the intermediate and final solidified zones. The experimental findings were analyzed in the framework of diffusion and convection controlled solidification, as well as liquid metal flow theories. The solute dependence of segregation features was related to the difference in solid-liquid partition coefficient and diffusion capability of each element in the liquid iron. Calculation of Reynolds numbers (Re) during the filling process, for both ingots, showed that higher filling velocity caused more instable movement of the liquid metal in the initial solidification stage, resulting in the modification of grain morphology, as well as accelerated solidification rate.