Thermal-mechanical behaviour during initial solidification in continuous casting: Steel grade effects

A transient finite-element model (CON2D) is applied to compute temperature, stress, and distortion of the steel shell during initial solidification. The model incorporates temperature- dependent properties, thermal shrinkage, phase transformations, and different elastic-viscoplastic constitutive equations for each phase (liquid, δ,and γ). The effects of sudden metal level fluctuations are simulated for different steel grades. Increasing the depth of a level drop increases distortion of the shell tip, curving it further away from the mould wall. This curvature is largest for ultra-low-carbon (ULC) and peritectic steels, and decreases for low- and high-carbon steels. This matches the well- known plant observations of the variation of oscillation mark depth with steel grade. The results suggest that the shape of the lower side of oscillation marks is governed by thermal distortion, which is greatly aggravated by level fluctuations.