EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Electrofusion is a foundry-like process at extremely high temperatures (1 850°C) to produce refractory blocks. The annealing of the ingot lasts several days/weeks. The blocks are composed of Alumina-Zirconia-Silica (AZS) and a header is casted above the block to keep the macro-porosity outside of the useful section of the ingot. As temperature lowers, a macro-porosity is created inside the header, due to density variation over temperature, and hot tears might appear along the block edges. Several criteria have been published in the literature to predict the formation of hot tears on steels and aluminum alloys but they have not been adapted yet to ceramic ingots. It is therefore relevant to combine computation software, that used such criteria, and experimental data about AZS refractories to understand better the annealing step.
The objective is to understand the link between the solidification step and the final quality of the blocks (macro-porosity and foundry defects such as hot tears) thanks to the 3-D finite-element software THERCAST®. The constitutive equations, determined from available experimental data, have been implemented in the THERCAST® software to model the deformations and stresses evolution in the block after its casting. The validation of thermal computations is made by comparison with experimental temperatures recorded in the mold during industrial ingot castings. Simulations are then run to compare different block geometries and material compositions.
The purpose is to better understand the annealing step for refractories thanks to THERCAST®, initially designed for steel foundry ; even if data adjustments are still needed to better fit the experimental annealing temperature curves. The long-term objective is to predict the feasibility of new industrial processes before testing them at industrial scale, saving a huge amount of raw material and energy.