Controlling mould-level fluctuations and friction in hypo-peritectic steel continuous casting through mould powder optimization: plant trials and thermodynamic simulation

The caster machine under consideration smoothly casts steel slabs of low-carbon steel grades (C < 0.08). Difficulties like abnormal mould-level fluctuations (MLF) and high friction coefficient were faced while casting hypo-peritectic steel grades (0.08 < C < 0.15). The initial action taken to mitigate the problem included a reduction in casting speed, which failed to eliminate the problem completely. Mould powder, being at the centre of the casting process, was looked into for a more robust and permanent solution. Subsequently, a number of plant trials were taken with different mould powders, selected strategically, to identify the most suitable one for stabilizing hypo-peritectic casting from this caster. Finally, the best powder for the prevailing conditions at the caster shop was identified to be the one with the lowest basicity (1.1) among the tried powders, contrary to the common assumption that only high-basicity (>1.2) powders are suitable for hypo-peritectic casting. Furthermore, why high-basicity powders failed, while the lowest basicity powder succeeded, was explained through thermodynamic simulation using FactSage 6.2. Apart from this, superheat was also optimized. 20–25°C superheat was found to be ideal for stable casting. Therefore, hypo-peritectic casting was stabilized from this caster with the new powder and optimized superheat.