Identification Of Cracking Issues And Process Improvements Through Plant Monitoring And Numerical Modelling Of Secondary Cooling During Continuous Casting Of Hsla Steels

A holistic approach to diagnose the occurrence of cracking on HSLA steel slabs and propose counter-measures to prevent them is presented. The approach consisted on plant monitoring, including direct temperature measurements in the strand with pyrometers. Extensive characterization was performed via thermo-mechanical tests and microscopy techniques which revealed combination of Widmanstatten ferrite, acicular ferrite and secondary phases that promote embrittlement during casting with a minimum ductility between 700 degrees C-800 degrees C (+/- 50 degrees C) which is responsible for cracking in this steel. Finally, 1D and 3D numerical models were developed to test possible cooling strategies which proved that reductions in water flowrate can have a positive effect in slab quality by avoiding the low ductility zone. Corrective actions included decreasing cooling to increase the overall temperature of the strand before the straightener to increase the overall temperature. Yet, some slabs still observed the presence of cracks which points at secondary factors such as high tundish temperatures > 1 530 degrees C producing cracking. Other secondary factors include strong temperature variations up to +/- 250 degrees C during measurements which would send the strand corners into the low ductility range producing cracking despite having a hot slab centre. Although these optimization strategies are particular to each caster and steel grade, a similar approach could be applied to address secondary cooling issues during continuous casting. The models presented are an ideal toolkit to analyse the influence of product size and operation parameters in combination with plant monitoring and extensive microstructure characterization to improve the quality and productivity of the process.