| Summary: | Thermal distortion during the initial stages of solidification is an important cause of surface quality problems in cast products. In this work, a finite element model including non-linear temperature-, phase-, and carbon-content-dependent elastic–viscoplastic constitutive equations is applied to study the effect of steel grade and interfacial heat flux on thermal distortion of a solidifying steel droplet. Due to thermal contraction, the bottom surface of the droplet bends away from the chill plate and a gap forms. It is shown that, regardless of the nature of the heat flux, the gap forms and grows the most very early during solidification (~0.1 s) and remains almost unchanged afterward. Increasing the heat flux decreases the time for evolution of the gap and increases its depth. When the carbon content is less than 0.10%C, the gap depth is very sensitive to the heat flux, but for higher carbon contents, this sensitivity is much weaker. The highest gap depths are predicted in ultra-low carbon (0.003%C) and peritectic steels (0.12%C), and agree both qualitatively and quantitatively with the experimental measurements. Thus, the current thermal-mechanical model, including its phase-dependent properties, captures the mechanism responsible for nonuniform solidification, depression sensitivity and surface defects affecting these steels.
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