Confinement effects on microstructure length scale selection in chill-cast stainless steel

Abstract

This study reports experimental measurements of spacing selection of confined dendrite growth in chill-cast stainless steel under transient cooling conditions. This phenomenon is also explored using phase-field simulations under non-steady state cooling conditions. Two phase-field models are employed, a ternary phase-field (PF) model where Ni and Cr are explicitly simulated, and a pseudobinary model which acts as a special case. Simulations reveal a strong finite-size dependence in the primary arm spacing (PAS) of cells and dendrites. This behavior is also observed experimentally within individual grains, where dendritic fronts evolve within parent grains that impose constraints on the solidification front. Quantifying PAS by a characteristic length ${\lambda }_1$, this metric is observed to exhibit a stick–slip behavior as the front advances, which corresponds to times in the solidification of slow (or no) change in ${\lambda }_1$ followed by a rapid increase in ${\lambda }_1$ caused by a succession of cell elimination events. The statistics of cell extinction are also analyzed, finding a correlation in the statistical time between extinction events and system size. Specifically, simulations reveal that the length of time of such PAS plateaus is stochastic, exhibiting a mean time that decays approximately exponentially with system size. As system size increases, this effect diminishes and a more monotonic relation between ${\lambda }_1$ vs. front speed is observed, consistent with classic geometric theories.