Experimentally-aided Simulation of Directional Solidification of Steel

Abstract

Dendritic microstructures are most dominant patterns in solidified alloys. The microstructural features of these structures control the segregation profiles of solute elements in the interdendritic regions, thus determining the mechanical properties of cast structures. In this study, a 2D model of solid/liquid interface instability in a low carbon steel was introduced, using the multi-phase-field software code MICRESS ® combined with an in-situ study of solidification in a laser-scanning confocal microscope. The use of a moving-frame boundary condition and a linear temperature gradient within the simulation allows further optimization of the solidification studies in the laser-scanning confocal microscope. By analysing the shape of the delta-ferrite grain boundary at the solid/liquid interface, in-situ and at temperature, it was possible to experimentally determine the Gibbs-Thomson coefficient and the solid/liquid interfacial energy of the alloy. The interface mobility of the solid/liquid interface was calibrated in the model so as to reproduce the experimentally measured interface velocity at the onset of interface instability. The proposed model was used to describe the morphological transitions from planar to cellular to dendritic modes during solidification and solute segregation under a variety of processing conditions such as cooling rate and temperature gradient. The importance of this approach is that the verified model has been used to extend the prediction of microstructural development to cooling rates well beyond what can be achieved experimentally and into the regime pertinent to high-speed continuous casting. Significant microstructural differences that arise as a result of varying processing conditions are discussed.

Study on Micro Segregation of High Alloy Fe–Mn–C–Al Steel

“…[21] Combined with the concentration field, the phase field model can be used to analyze the effect of dendritic morphology on the distributions of solute elements during solidification. [22] Senk et al [23] investigated the microstructure and micro segregation behavior of the Fe-Mn-Si-Al high manganese steel using the phase filed model and the simulation results were in good agreement with that of the experiment. Alves et al [24] revealed that the phase field model was a great method to investigate the micro segregation of Mn with high Mn content (%23 wt%).…”

“…In general, the rate of rejection of solute at the interface is proportional to the growth rate. The rejected solute must be carried away by diffusion down the interfacial concentration gradient, and this therefore becomes steeper with increasing growth rate . High cooling rate reduces the solidification time and limits the back diffusion of Mn in solid phase.…”

“…The rejected solute must be carried away by diffusion down the interfacial concentration gradient, and this therefore becomes steeper with increasing growth rate. [22] High cooling rate reduces the solidification time and limits the back diffusion of Mn in solid phase. On the other hand, increasing cooling rate can promote the formation of the secondary dendrite and reduce the SDAS.…”

“…One dimensional mathematical model basing on the scale of the secondary dendrite arm spacing can describe the micro segregation behaviors of solute elements, and the phase field method is a good way to demonstrate the microstructural evolutions . Combined with the concentration field, the phase field model can be used to analyze the effect of dendritic morphology on the distributions of solute elements during solidification . Senk et al investigated the microstructure and micro segregation behavior of the Fe–Mn–Si–Al high manganese steel using the phase filed model and the simulation results were in good agreement with that of the experiment.…”

Multiscale Discrete Crystal Growth in the Solidification of 20SiMnMo5 Steel

“…Recently, the crystal growth in the solidification of metal alloys can be observed in real time by confocal scanning laser microscope − or synchrotron radiation. − The confocal laser microscope can observe the growth phenomena on the surface of the sample. And synchrotron radiation can observe the crystal growth in a slice sample.…”